They just announced a Young Squadron book for the Heroes Reborn thing, and I guess that is essentially the Young Avengers of that universe. No actual YA characters announced so far, though.
The Young Avengers technically wouldn't even exist in the Heroes Reborn universe because the Avengers don't exist there either. But now that I think about it, I'm afraid some members wouldn't even be born, because if the Avengers never existed, then Wanda and Vision never met. Same for Mar-Vell and Anelle (they only ever met because the Kree/Skrull War was an Avengers story). So that's a timeline that potentially doesn't have Billy/Tommy/Teddy. Maybe Mar-Vell and Anelle would've met in different circumstances, though, but that leaves Teddy's origins in a very unclear place. Maybe Billy Kaplan and Tommy Shepherd would be born, but they wouldn't be the reincarnations of William/Thomas Maximoff, which would wildly change their life story. Cassie might've died if her father never became an Avenger to save her life. Eli might've been born, but his grandpa wouldn't ever have been Captain America. Kate probably would still exist, but it's unclear what would've happened to her without YA/Hawkeye. Not sure what would've happened to a young Nate Richards. If Wiccan never existed, then America would've never existed either, because he created her world. It's interesting thinking about all the butterfly effects....
Saying ''it's a mystery'' and telling people to read the book to find out does make it seem like it is something that will be addressed. She could've simply not said anything if this isn't something that's a part of the story. Or she simply could've said ''we won't be explaining this'', which is just being honest and not giving any spoiler. But yeah, I hope it's something that comes up later. I'm just not very hopeful because, well, it's Tommy.......