Development Hell: It was announced in 2011 that Screen Gems had acquired the movie rights to the series and planned to make one with Kyle Ward attached as screenwriter. Nothing was heard from it since the announcement.
In regards to 2's placement in the chronology of the numbered titles. While the placement of 3's manga, 3, 1, TAS, and 4 were easy enough to arrange, Capcom was so wary about 2 that it wasn't until the Devil May Cry:3142 Graphic Arts artbook that gave fans a resemblance of a timeline. With 5's announcement at E3 2018, it was initially stated that the order was 3 > 1 > TAS > 4 > 2 > 5, but later on, Capcom streamed a summary recap on February 6, 2019, that changed the order where the timeline became 3 > 1 > TAS > 2 > 4 > 5 instead.
Gene. He also doubles as a (decidedly more lighthearted) expy of Kenshiro. Capcom would later take notes and base Nero partially off the former.
Bayonetta and Jeanne are both Gender Flip examples. The two ladies are snarkers that both fight with swords and guns, taunt their enemies, and the latter even has white hair and dresses in red. The only differences is that they are witches that fight angels. note They fight demons in the sequel.
Kagura is another gender flip example that is very Stripperific and arguably an expy of the DMC3 incarnation. A Half-Human Hybrid (Dhampyr in this case) that's young, snarky, taunts, and likes to show off. It fits the bill.
Vicious is another Dante expy; dual wielding guns, wearing a longcoat with no shirt and surviving being stabbed through the heart. Complete with a cocky and trollish attitude, as well as not even hiding the fact that he's thought of as a bad guy.
There's a bunch of DMC materials that were never released outside of Japan, including: a good amount of artbooks that go into further details on things that got left out, two drama CDs for The Animated Series that serve the same role (and fill in some of the blanks between DMC1 and TAS), the two-volume novelization of 4 subtitled Deadly Fortune, and the tie-in/prequel novel for 5 titled Before the Nightmare.
For a more minor example, while Devil May Cry 4: Special Edition was released digitally around the world, physical copies were only released in Japan and other parts of Asia. Somewhat subverted, however, as those who live in other countries can still purchase a physical copy online, as there is an English option available and the PS4 and Xbox One both aren't region-locked.
The pachislot machines (a combination of a traditional slots machine with a pachinko machine) for 4, Devil May Cry X: The Last Judgement (the "X" pronounced "cross"), and CR Devil May Cry 4. The first two, produced by Enterrise, used the in-game assets that included additional scenes and lines not seen in either the original game's release or the Special Edition, to which online comments have noted that DMCX somehow tied Vergil's story much tighter into 4 compared to the Special Edition release.
In a rare inversion, the Collector's Edition of 5 that included a miniature version of the van seen in-game as well a small artbook was restricted to Amazon US and Canada, and the US Capcom online store.
The Visions of Vspin-off manga tells V's point of view prior to the events of 5, but the online manga service it's being released on is region-locked behind Japanese ISPs unless one uses a VPN.
Dante's voice actors, due to the first game being recorded in Toronto and the later games being recorded in Los Angeles. They didn't bring one back for a second game until 4 (see the Characters page for the full list). It wasn't until Reuben Langdon (Dante's Ink-Suit Actor) voiced him in 3 that a VA stuck. Subsequently, Langdon went on to reprise his role in 4, The Animated Series, and 5, the latter two causing a massive moment of fandom rejoicing when announced.
This is made even more jarring if one considers Dante's appearance as a Secret Character in the PS2 version of Viewtiful Joe. Although it came out a year after 2 (where he was voiced by Matthew Kaminsky), Dante's voice actor is the same as the original game (Drew Coombs). In other words, it went from Drew Coombs, to Matthew Kaminsky, back to Drew Coombs, and then finally to Reuben Langdon, who has been voicing Dante ever since 3.
This doesn't even factor in Dante's other out-of-universe appearance as a Guest Fighter in Shin Megami Tensei: Nocturne, where Dante's voice actor is Kaminsky again. However, it's just a case of reusing his grunts and warcries from 2. The HD rerelease of the game would properly give him a voice, that of his now-standard actor Reuben Langdon.
Dante was Darrin'd again for the reboot, this time being voiced by Tim Phillipps. Granted, that Dante is technically a different character with a different personality, so keeping the same voice actor would have been odd.
It would seem that out of all of the recurring characters (what few there are), only Lady has kept her VA (Kari Wahlgren). At least until DMC4:SE, where Kate Higgins assumed the role, rerecording all of Wahlgren's lines along with providing new ones for additional cutscenes and Lady's playable outings.
Throw It In: The enemy juggling mechanic was born from a glitch that accidentally allowed juggling in Onimusha: Warlords. The glitch was fixed before Onimusha's release, but was so awesome that Capcom added it to to the first DMC and later became a staple for the series.