We can do this now, but I don't think the user experience makes it worth it compared to casting. Bandwidth limitations require lower frame rates and responsiveness, which is fine for video but bad for interactive apps (most phones are native 120+hz + VRR_. But re-encoding video is (processor & battery life) expensive and probably lower quality than the original stream.

People who do this a lot probably just use a DV adapter (maybe it just works with USB-C, but I haven't tried it) for native apps, or casting for streaming video.

Right — I would have hoped a while ago already that we transcend past the notion of an endpoint device. A tablet, a laptop, or a phone should all just be entry points to access my one OS instance.

You could think this a bit further still, and have all kinds of devices offer an interface to nearby endpoints with a display or controls, establishing connectivity automatically.

Apple does this right now. I use AirPlay to extend one laptop into an older laptop so I can have 2 displays when I’m away from home

I mean you kinda can do that now.