Except it would show exactly in the order of the tabs (so armor and weapons still get fumbled together). So I ask again, what would be the point of that if we have tabs already. If it's for stuff you mentioned like knife on pillow being hard due to no knife on ingredients, a better fix would be to add it there (like how repair hammers and identifying glasses appear amongst weapons).
Again, it's working AROUND a problem, rather than fixing the problem. And in the end doesn't help much to made the UI apparently less "cluncky" than actually fixing it would. Cause really, do you prefer going to 100 items to combine them or 30? Your suggestion is basically asking for #1 and I say "don't bother, if you fix the problem, there's no need for it, and you've wasted valuable development time. Time that could even went to fixing the problem"
It's funny that you on the one side completely object the idea of a quest item tab but on the other side even claim that all craftable items or ingredients should have an own tab...
You know, that's a contradiction in itself. And an inventory tab which includes all ingredients for crafting (weapons, armour and everything inlcuded) would be approx contain 80% of your inventory items anyway, only with the difference that it's against the old-school hardcore attitude to not make the life of the game any easier but to keep the exprience as clunky as possible...(a bit ironic, sry).
