I mean I'm more interested in PC handhelds in the future because I think AMD will incorporate FSR4 in future mobile chips, as they're already trying to backport it to RDNA3 GPUs.
At the very least, I would imagine they could do something with Valve, since the Steam Deck uses a custom chip. If Valve wants to have a generational uplift, having an upscaler that doesn't ruin image quality like older FSR would help significantly, and have benefits for when you connect it to a larger display like DLSS is doing for Switch 2.
Either way, I'm excited for future PC handhelds, because we're seeing high refresh VRR displays happen, next Steam Deck should have the juice to do PS3 emulation with better battery life than ROG Ally, more will likely support external GPUs to last past their prime, and AA to indie games will get even better battery life.