Please check these 3 videos about what I told about moving start/end position and you might get an idea how powerful it could be. This is a simple reaktor sampler someone made by my request. Besides looping like basic sampler it can also loop a region without changing the pitch of the sample, but by changing loop region. So it can play notes by changing loop size, which gives different interesting result.
Also the cool feature he made just by himself is a pitch slide. I think it is somewhat similar to a bend modes in Serum. It makes a pitch slide inside the loop, not a pitch slide of the playing note, but only inside the loop, like bending the sample inside the loop.
So the problem with this sampler is that it can't play smoothly when changing the start position. It creates clicks. I hope videos are presentable enough to show how powerful this thing could be.
I call it Scan Synthesis(cuz the loop could slide over the sample). Had this idea back in the end of 90's and wonder why no one made it. I think the idea is very on the surface in looping in samplers themselves.