Ok from what I gather the retroboot version of the Legion more or less restores the Legion sometime prior to the 5 years later stuff. So I have some questions.
1. Just how far back does it go? Did these characters go through the Magic Wars storyline just prior to the 5 Years Later stuff? I guess my main interest is whether Cosmic Boy's brother Magnetic Kid still died...for some reason that death always annoyed me.
2. Where does Supergirl fit in? I think she was killed in the crisis prior to the 5 Years Later arc. So many events in Legion of Super-Heroes vol 3 have been altered I assume.
3. Where does the pocket universe Superboy fit in? Or rather how did things differ with the storyline where he was killed off presumably not happening? If the real Superboy had adventures with the Legion then there was no PU Superboy so he didn't have a funeral, a faction of the Legion didn't plot revenge against time trapper and the time trapper didn't get seemingly destroyed by the Infinite Man...and the real Superboy either did or did not continue having missions with the Legion.
4. Garth and Imra's kids...one of their sons was Validus...that still happened right? But the twin daughters from the 5YL era never existed right?
5. Ayla and Vi. Where does their sexuality end up with all the rebooting and retconning. Do Ayla and Vi still like women or are they back to being heterosexual again? I think the gay thing came up during the 5YL suff.
6. Element Lad...so is his girlfriend Shevaughn still a transsexual or is she back to being a real woman? He found out she used to be a dude in the 5YL stuff
7. Does Leland McCauley still have a niece (Celeste) or does she no longer exist?
8. What happened to the real Glorith? I assume she wasn't the one on the team but her 5YL history never happened...but she existed prior to the 5YL stuff.
9. Is Laurel Kent still in continuity with the retroboot? I'm assuming the Laurel Gands from 5YL and the post zero hour reboot don't exist anymore. Wikipedia mentions there was some version of Laurel that popped up with Kent Shakespeare from the 5YL era around 2011. So are they back in continuity or was that an alternate future that had nothing to do with the Legion?
I am not the Legion expert but since it was the Cosmic Boy 4-issue series that tied into Legends that first made the Legion realize that their history was wrong, I'd say this is a good enough place to make the break for the retroboot.
In Legion of 3 Worlds, a Final Crisis book, both Laurel Gands and Laurel Kent appear (for a panel or two).
No idea what effect the New 52 had on it.