While this is true (even without an emulator) that you can connect Mobile + PC today either via local network or via IP (Port Forwarding etc) - in full disclosure, I am in the middle of a playthrough with my family where we are hosting on a local PC and connecting on a combo of phones and other PCs - that does NOT mean that it will be approved by first parties (Microsoft, Nintendo, etc) for other platforms.
We have tried to be clear that we cannot make any promises as to if we will be able to get everyone to Crossplay... or what form it will take. We are happy with our plan, but even if we get it all to technically work... the final decisions don't sit with us, they sit with the platform owners. They can say yes or no for any reason they choose.
So yeah, wish us luck, we need it!