As a Warframe vet of 6 years now I have something I want to suggest. No I do not mean "I am a vet and by default correct in everything I say." What I mean is that it is just something I have noticed would be a very advantageous feature. An observation. Basically: The ability to transfer work you put into base frames to the primed version of the frame.
Allow me to illustrate. I got Wisp asap on release and put an aura, umbra, and a few base forma into her. Something I realized though, like I knew this already but, when her Prime comes out. I am going to have to level the frame again. Now I understand that this fact is not hidden; DE use it as "free" content. However, The issue this causes is, like with Wisp for instance, the only reason I bother putting much effort into most frames is because I am really hyped for them. With Grendel, I liked him a lot, he was a neat concept, but not enough to bother formaing him at all just because I do not know if I would like/play him enough to even bother putting in two (a good number of frames can be decent with just two forma, not sure if this applies to Grendel too actually; not the point though.) knowing that it would be wasted.
Imagine if you could opt to use a current base frame to significantly reduce the amount of time and money it would take to build a prime frame. That way base frames do not just end up in the waste bin after you went through all that effort, which feels really bad btw. When you do this, all the forma and potatoes remain as well as all that time and effort.
Things get wasted currently when transferring from a base warframe > a primed version
5.Credits (technically a resource, but worth mentioning separately)
Making it all transferable, however would:
1. Add a sense of progression
2. Motivate people to get more hyped about new Warframes (currently there are, at least personally, reservations with new frames because of that inevitable prime variant factor)
3. Motivate people to get more hyped about new primed frames (because starting over from scratch would not be a concern)
4. Help prevent burnout