This is an idea that came to my mind, I'd like to know your thoughts about it.
I was looking in my inventory all the warframe mods I have, most of them haven't ever been used, and most won't ever be, the reason? The lack of space, if you keep all the abilities installed then you have only 6 slots, so you fill them with the most necessary mods, and sometimes even useful ones are left out. Some people then take off some 'not so interesting' abilities to give room for other mods (I do it), mischaracterizing the frame somehow.
For me that's all wrong, the frames abilities are part of who they are, you should be able to keep them and without the cost of mod slots. If the abilities mods were extinguished then we would have 4 more slots to fill with useful mods, or even those interesting (not so useful) mods that have no space in anyones build, the abilities would be incorporated to the frame with no need to install them, this would incentivate people to use the not so amazing abilities (like many number 1s) as they would be in hand with no cost. In the other hand a very nice side effect would be not having those mods in the drop rates anymore, imagine those hundreds of slash dashes droped replaced by other mods, and whenever you found or got by transmutation a rare mod it wouldn't be an useless ability :)
About the effects by leveling up the ability mod rank with fusion cores, they could be acquired as you level up the warframe itself, as it would be part of the warframe.
So what do you think?