How to have one f-curve per keyframe or for multiple channel?

Hi there

I am fairly new to Blender and so far i must say i love this software, it can do so much!

But anyways, here is my problem : I am trying to have a single f-curve, function, or whatever you wanna call it between 2 frames or multiple channels instead of one per channel. Something like a normalized function (between (0,0) and (1,1)) where the X axis represent the time between 2 frames and Y the influence of the second frame.

It would make it much more easier to get more realistic transitions between animations and all sorts of other cool techniques.

Being able to tweek individual channels is neat but it seems more like the exception than the rule, at least in my case.

Is spherical interpolation between quaternions a thing in blender? It seems to be the norm when dealing with quaternions but i can seem to get it in Blender.

Cheers