The new Flash cowl covers part of Barry's jawline. Given that he's now attained celebrity status, he'll need to hide his identity more thoroughly, to the point where he'd wear a face covering that not only hides his features but also distorts them.
Besides the foreshadowing elements mentioned in the main page, the use of the song "Pedro Navaja" in the film has another layer of commonality with the movie, in that it is a famous example of Lyrical Dissonance in its original version: an extremely catchy and upbeat tune that tells a very dark story of murder, just like The Flash is the most overtly silly and comedic movie in the DCEU, but with a very dark plot-line.
Zod's more subdued and flat demeanor in the movie, in contrast to his hot-blooded temper in Barry's original timeline, make sense with The Reveal late in the movie that he dissected an infant Kal-El to get the Codex, only to discover the Codex was elsewhere still. While Zod is ready to do anything to save his people, his now-pointless murder of a Kryptonian child, and his former friend's at that, would probably shake him nonetheless.
Superman's importance to the DCEU. Supergirl may be strong, but she is no match for Zod and his army. Without DECU's most powerful superhero, their world would stand no chance against juggernauts like Zod and Darkseid.
89 Batman and Supergirl's performance in the final battle. Batman has been out of action for who knows how long and is using outdated equipment; while he is otherwise the most competent and experienced of the heroes, he is also punching well above his weight. On the other side of the coin, Supergirl only just got her yellow sun induced powers, and her rage at Zod for killing the infant Kal-El could only get her so far against Zod; the general might not achieve the full potential of his powers like he did in Man of Steel, but he is still an experienced combatant fighting with his emotions in check.
Alt Barry claiming to his roommates that Prime Barry is his cousin, despite them sharing a name may be a homage to DC Rebirth, which used this concept to restore the classic red haired Caucasian Wally West without erasing the New 52 black Wally.
Nora's killer is never shown, but if we assume it is the Reverse Flash as per the comics (and also as depicted in Arrowverse), then the Alt 2013 timeline might explain why she is no longer dead: When Zod wins, which he inevitably does in this timeline, he will end up killing all humans when he terraforms Earth. No more humans means no one to give birth to a future Eobard Thawne.
On the Back to the Future movies being mentioned to star Eric Stoltz instead of Michael J. Fox: while the recast of the real-world didn't happen, the movies are implied to be the same hit success as in our world, even though the recast is usually named as one of the big reasons for it's success, so... what gives? One possible answer is based on the reason for the recast in the first place: the plot of the movies, especially the ending of the first one can easily read as an existential drama (essentially, Marty comes back to live among complete strangers, more on the appropriate Fridge page) and Eric Stoltz refused to see the whole film as anything else, as opposed to the light-hearted comedy the creators intended - which is why the role was recast. In the alternate timeline it is entirely possible that Zemeckis and Gale decided to roll with Stoltz's idea and revamp the whole movie as a drama about getting lost in time and it succeeded.
How exactly did Barry learn that there are certain things (like babies) that he can't move quickly?
He was likely just using this as a general example of how it would kill living things and had babies on the mind.
Barry also implies to his younger alternate self that after a few mishaps while still getting used I his powers he decided to do “the homework” on how his powers work in conjunction with other things and other people so he could avoid an incident like that.
Just the fact that Batman is vulnerable to the Lasso of Truth. BATMAN. It's not just his own secret identity at risk, it's the secret identities of the rest of the Justice League. And his plans on how to kill them all.
Dark Flash had to create a time paradox just to bring himself into existence. Now remember that the Flash had to actively remove that fated can of tomatoes from Nora's shopping cart just to "reset" events. It's entirely possible that the original DCEU timeline was one more paradox. All of a sudden inescapable events like the death of Superman and the Knightmare future feel like they could be the fault of one guy just to ensure he'd become a superhero.
The 1989 Batman universe Earth is actually doomed to be terraformed into a new Krypton, making it All for Nothing.
On the other hand, Bruce's explanation about how time travel worked when talking with the two Barrys suggests that his Earth merged with Barry's when Barry ran back to change history, so it's also possible that the original version of this Earth remains intact and safe after Barry prevented his original changes to history.
