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Would be nice, if some older Xbox classics (which don't move hardware anymore) get ported to Switch for a good handheld experience.
Halo MCC (or at least Halo 1 + 2 Anniversary Editions and Halo 3) and Fable 1 + 2 would be good candidates.
You can already play Halo 1 + 2 on a GPD Win handheld, but only the old versions:
With the Halo MCC announcement for Steam (and not only the Windows Marketplace), they lose exclusivity for Xbox anyways, so an additional platform with a different focus (mobility) wouldn't hurt much.
On the other hand, there are already great Nintendo games playable on non-Nintendo hardware:
https://nintendo.fandom.com/wiki/Nvidia_Shield
So a port of Super Mario Galaxy or Twilight Princess to Xbox (after or simultaneously with a Switch port) ain't impossible either.
