I understand that some aspect of the Mirroe Universe and other races have been touched on. Still, they are not fleshed-out to the point that they cannot be tweaked or expanded. I agree with an earlier poster on that Abrams seems to want it to both ways. Personally, my opinion is pick one, dude. A complete “reboot” or a remake - pick one. Hell’s bells, they could have just tried an entirely new storyline with new characters within the broader universe - good writers would find a way to make it work. Heck, even go the AVP route and have Gorns versus Tholians! ;-). Instead, it seems as though the writers chose the lazy route - take accepted characters and change things just enough to give the appearance of orginality but with damned little truly fresh.
A lot of the history or the Mirror Universe has been fleshed out in those episodes. And really it’s a pirate universe, that gets boring fast, hard to find room for external plots when it’s important to have your main cast trying to kill each other every movie.
Reboots are about having it both ways, that is why you do them. Keep the concept ditch the canon. New stories within the broader universe still have to drag around the canon, if you do a Gorns vs Tholians movie somebody points out how the two could never have met due to some single sentence somewhere. That’s the canon problem, it chokes stories to death.
The writers took the smart route the “no we aren’t watching 28 years of TV and 10 movies most of which actually suck just to write one damn movie” route. Reboots happen all the time, every 3rd freaking James Bond movie is a reboot, Trek fans just need to suck it up. Because really, their whining about the sanctity of a canon that never really even existed is WHY a reboot HAD to be done and should have been done 2 or 3 times by now.