@KeyJ having had to do part of it in SW to work around HW bugs (not with ASTC though, only BC1-7!) most of these are not that bad if you "lower" them the way the HW already does internally.

i.e. trilinear, aniso etc. all turn into a sequence of weighted bilinear samples added onto an accumulator and the last one has a "I'm the final one, return me!" bit.

Cubemaps _mostly_ turn into logic in the shader to select the face and then regular 2D texture sampling (except for corner texel filtering)