what you got against drop in nuts ?

I actually make my own for non critical add-ons and mods and slot a 3mm nut into the plastic part :-)
The tiamet diamond dust filament makes fantastically strong drop in nuts. And polycarbonatre would as well.
have to try that :-)

the spring loaded ones are a good idea. the main hassle with pre loaded nuts is the fact that they slide all over the bloody place.

So what high temp filaments are you looking at ?
And would some of these applications be car related by any chance ;-)

Everything I can think of needs a pretty hot enclosed build volume.
The minifactory peek printer basically prints inside a hot oven.