What happens if you try to downloop/ kiteloop a foilkite? I'm thinking it would just collapse as it comes fully forward in the wind window.

Ummm........ It loops!.....
Typically a bigger, Slower more powerful loop.

They just loop. Like you'd expect. You Hyperlink will be awesome for looping- try it on the foil next time you are wanting to gybe downwind.

Sounds like you need a c kite Simon

Doesn't seem to bother these guys

Kitelooping or downlooping foil while snowkiting is the basic thing to learn.
On the water, all the hydrofoil riders downloop a lot during manoeuvre.
Some riders also do proper jump kiteloop on twintip.
So yes foil can loop, slower and more powerful than inflatable for sure.