theres a lot of builds i still feel somewhat constrained even without using an augment, that being said, i don't necessarily want an "augment slot" anyway, TBH im guessing DE is going to eventually make more augments past already having 4 for each ability on some frames, and with that its only going to get harder, having a system in place where you can simply upgrade your abilities to inheritantly be the augmented version for a resource is probably the better move in the long run.
For example, you have a whatever augment like capacitance for volt right? normally you have no reason to ever run it because he has better augments, like shock trooper. However, if you had the means to simply upgrade all your abilities to the augmented versions without using mod slots, you could totally make use of all of them without having to only use the overall BEST one.
Remember when the abilities themselves were mods on the frames that you could equip and un-equip? a lot of people wanted that to change, and eventually it did, and it changed for the better overall because it just felt weird to not have a warframe with all of its abilities present, even if said abilities werent always the best.
Personally i think a system like this would encourage the use of the lesser used augments.