Contest Winner Cameo: Several times. 5th Mix has "Paranoia Eternal" (which won a remix contest). The U.S. versions also had winners from a music contest held in conjunction with BroadJam in later versions, which led to songs such as "EternuS", "There's a Rhythm", "GO! (Mahalo Mix)", "Grandolin", "Race Against Time", "Till The Lonely's Gone", and "30 Lives" appearing in Universe games (and SuperNOVA 2 and X too in later instances)
DM Ashura, the winner of one of these contests, became a Promoted Fanboy by the time Universe 3 came around. Said game had a bunch of songs by him, and even a collaboration with kors k of Beatmania fame.
His Max remix, Delta Max, became Ascended Fanon as well. The song originated as the special extra stage on a StepMania machine at the now-defunct Tokyo Game Action arcade in New Hampshire. But then, it became official on Universe 3, and even hit the arcade version on X2.
One DDR player celebrated his 800th AAA rank by posting a picture of it on his Facebook timeline. A Facebook page picks this image up and posts it, congratulating him...but erroneously calls the song "Xepher Tatsh"◊. note The song's name is simply "Xepher"; Tatsh is the artist. The most embarrassing part about it? Said page is the official DDR Facebook page!
Even "better", the same page mistakes◊ a Pump It Up cabinet for a DDR cab. The admin of the DDR page mistook DDR's rival series (which has had a long legal history involving Konami, to boot) for DDR.
Executive Meddling: Due to some form of expiring license for the vocals, a new version of "Dynamite Rave" was recorded for the international arcade versions of DDR X (which also made an appearance on Hottest Party 3 as a "new" song with completely different charts, alongside several other similar remakes)
The infamous Raw Thrills DDR X cabinets were also a form of this due to cost concerns; the game even had location tests and convention showings in a Japanese cabinet (although, sans the light sticks in later tests)
Inverted by DDR X3's initial extra stage song "Amalgamation", which first appeared in a DLC pack for jukebeat, the English-language version of Jubeat
Name's the Same: There are two different songs named Fantasy, one which debuted in MAX and another which debuted in MAX2. Yes, they both made it onto Extreme too.
There are two different songs named Stay, one which debuted in MAX2 and another which debuted in Extreme.
The PlayStation game Extra Mix (which has the Solo sub-series songs and the songs new to 4th Mix Plus) has three pairs of same-named titles: I'm Alive, Together Forever, and Sky High.
DDR Ultramix 3 for Xbox has two songs named Come With Me.
No Budget: Betson by far. Since SuperNOVA, cabinets have been built on a very slim budget. The cabinet problem got even worse on X; while Asia got an extremely nice new cabinet design with tons of LED effects and the ability to retrofit legacy cabinets, everyone else had to buy a new Raw Thrills cabinet, which looked like a cheap, bootleg version of the Japanese design with elements of the Guitar Hero Arcade cabinet. They infamously featured poorly-built pads (which, just to show how lazy they were, were covered with one piece of metal with holes in it, as opposed to the traditional array of square panels), a weak sound system, a laggy monitor, and navigation buttons on a bare, metal panel.
Some of these issues seemed to have been rectified upon the release of X2 (which had a more traditional pad design, along a few more decals for an added touch), but players still reported pad problems. The distributor claimed that they did not release SN 2 to X hardware upgrades internationally because it would be too much for operators to handle. SuperNOVA and In The Groove 1 needed them too, yet operators managed; What gives?
No Export for You: After Dance Dance Revolution USA (which was a fork of 3rd Mix) was released, no new arcade version would be released in America until SuperNOVA, eventually leading to almost every other arcade importing Extreme. Even Europe got some in between with Dancing Stage EuroMix 2 (which had songs from MAX and MAX 2, and a design based off MAX 2) and Dancing Stage Fusion (in turn based off America's Extreme CS; it was the first PlayStation 2-based arcade DDR game, setting the stage for SuperNOVA. It was also the one making a cameo in Madonna's "Hung Up" video).
The Ultramix and Universe games were also never released in Japan. Some songs from Ultramix however, did get dispersed through several other titles, including DDR Festival (based off Extreme US) and STRiKE (based off Extreme 2), and a number of Universe 3 songs made an arcade debut on X2. While the first three Hottest Party installments got localized versions for Japan, Music Fit (Hottest Party 3 JP) was the final console DDR game released in Japan ever. In fact, Konami has all but given up on making new versions of arcade Bemani titles on major consoles in Japan (except on portable devices, and even some of those are outsourced). Most of the new songs on X3 vs. 2nd Mix were from Hottest Party 4/DDR 2010 and Hottest Party 5/DDR II (X3's interface skin was also based off the latter of the two, but modified to work on the DDR X engine), inverting the traditional struggle of America waiting from songs from the arcade release.
With no international release for X3, the arcade DDR landscape is back to how things were before SuperNOVA, except with the added complication of e-Amusement, again (though these issues are in no way exclusive to DDR). DDR 2013 is only available as a leased rental with revenue sharing (like many other Japanese arcade games of the era), making importing even less viable. Though there may be hope, as Konami seems to have made an ally in the American locations of Japanese arcade/bowling chain Round1..
Playing Against Type: PARANOiA ~HADES~, considered by many to be one of the most unsettling songs in the series, is an instance of this. For those who don't know, αTYPE-300 is Jun, writer of Happy Hardcore tracks such as SUNKiSS ♡ DROP, Raspberry♥Heart, and TRUE♥LOVE. How can one artist create two completely different styles? A simple trip to the underworld will do that to you.
Revival by Commercialization: Earlier versions of DDR brought dance music musicians Smile.dk, the late Captain Jack, and others to fame. The former gained enough fame to perform in several different countries, including the U.S.
What Could Have Been: The trailer for a 2009 DDR game on Xbox 360 and PlayStation 3 (which would have accompanied X2 PS2 and Hottest Party 3) showed a revolutionary new face of DDR; with 3D stages closer in style to Guitar Hero, a themable interface, DLC from every arcade DDR game, "Octo-Move" 8-panel mode, mainstays such as Edit Mode, and more. But somehow, it basically disappeared after E3, and was shoved aside in favor of Dance Masters. But, when news of a PS3 version re-surfaced in 2010, fans hoped it would finally be the game they were hoping for. What they got just threw everything out the window: it was built off the DDR 2010 content (The least said about that one, the better), 8-panel mode was only on Challenge charts (with a very confusing layout that shoved the corner arrows in the same lanes as Left and Right), and it did not have the same extent of DLC as originally promised (though to be honest, they tried at least).
A Solo 5thMIX was planned and some 6-panel charts had been written for it when it got scrapped. Speaking of Solo, Solo 2000 also had unused files for a "Dancing Stage Solo", indicating a European release was planned but scrapped.
Knowing how many people hate the interface of DDR Extreme U.S., pre-release screenshots actually showed using the arcade version's interface.
Early screenshots of Extreme 2 showed "Tunak Tunak Tun" (yes, that song. That song by that one Indian singer whose music video involved an army of clones) as part of its soundtrack.
The Dancemania remix of the theme song from Final Fantasy VIII was supposed to appear in 5thMIX, but they dropped it at the end.
Devil Zukin was originally intended to be a playable dancer in X.