I feel like they've been trying to do this with wifi. Right now (in macOS) I see "Personal hotspot" "Preferred Networks" and "Other Networks" (which requires clicking to show).

One AirPlay solution I've seen is a pop up when you physically put your phone next to HomePod.

I really, really like connectivity between non-linked account. It's been really useful when going to those corporate "business centers" and you want to send over a doc to print or visiting friends.