wouldn't that require pretty hefty active cooling, which doesn't fit so well with Apple devices?

It would be great if they did it the eGPU route with TB4, in a slick package

This is more for the Mac Pro line. Not so much the laptops.

We’ve only see the Apple equivalent of the i3 with integrated graphics. It’s going to get interesting over the next several months as Apple unveils their middle and upper performance solutions.

Does that mean they will actually produce a laptop with adequate cooling? Might be worth looking at.

I own an M1 Macbook Air. At its hottest, it's a fraction of the "normal" heat that my year old Intel based Macbook Pro runs at.

To get the M1 warm, I need to be charging it while also playing an Intel based game like the latest Subnautica, with the machine on my lap. Even then, it's not as hot as my Macbook Pro gets while unplugged and browsing the internet.

No. According to rumours: the high-end 64-128 GPUs will be exclusively for the Mac Pro and the MacBook Pro will have 16-32 cores GPUs instead. It think it's fair to assume that we won't see much changes with the cooling for their laptops.