Will there still be some way we can see in one place what's required for mqc/comp/trim now that those don't have a category?
Yep, the Completionist category now only (other than the Feats subcategory*) contains the meta achievements for max, quest, MQC, comp and comp(t) capes.
The reqs for those cape metas are listed in alphabetical order.
Just click a req for the selected cape and it'll jump you to wherever in the system that achievement is located.
So the cape metas are basically an index that'll easily help you find their requirements to complete. :)
*Completionist->Feats is where all the 'hidden' achievements go. Previously these were invisible until you completed them. Now every achievement has a tangible presence in the system, so 'hidden' achievements have generic 'the details of this achievement are hidden' name and description until you complete them. So at least it's clear how many Feats there are. And they're bundled in one place so if you're not into chasing Feats, you can safely ignore them.