This has been thrown around as an idea for awhile now, and I think it's got some merit. I think Pokemon Z-A and Metroid Prime 4 will end up cross-platform like Twilight Princess and BoTW were for their specific gens. Prime 4 will be availaible and able to run on OG Switch, but I think Prime 4 could be a good baseline to show off the Switch 2's superior hardware and graphical capablities.
I think if we go another June Direct without Prime 4, it's gonna be cross-gen.
I also believe they've been sitting on Mario Kart 9 since before the Booster Course pack got announced. I think it's incredibly likely to be a launch title imho.