Sea of Thieves might have a presence next gen (Maybe through backwards compatibility or as its own nextgen version to launch with gamepass and such). Battletoads will be cross generation (They said 2019 in the teaser).
Crackdown 3 should be in the same boat as SoT.
Based on developer comments, I think they're skipping 2019 for Forza, and instead thinking of something different and big (Project Gotham Racing), or they are just giving an extra year for Forza 8 in 2020. Then FH5 in 2021, even though FH5 would be a killer launch title that would destroy everything Sony and Nintendo have to offer. Maybe Forza is going to enter a 3 year develop cycle?!?!. (The games are getting bigger by the year, but the time limit to make them isn't).
Halo (6) Infinite and Gears 5 might be cross generation (I'm betting it will just be Gears 5 being cross gen though). H:MC and Gears Ultimate also would be a fine edition at launch.
The gap from SoD 1 to SoD 2 was huge, so a State of Decay 3 launching within the first year of the Nextbox would be a stretch, but their owned entirely by Microsoft now, so they gotta be working them like a machine by now.
inXile has to be doing Wasteland 3, it is their most popular IP that Microsoft can milk and toss onto Gamepass.
Some sort of Age of Empires has to be a definite release, with them now fully supporting Mouse and keyboard, the game now has no reason to not have a presence on the Xbox store and in Gamepass.
Cuphead, and "Ori and the Will of the Wisps" should see an upgraded re-release.
It would be dangerous for them to shoot the load from all their 1st party devs in the first 2 years though. I wonder what 3rd party's their going to get on board for exclusivity (If any of them actually want to take that risk again). Is it too late to ask for Scalebound?.