Alright, but wouldn't they just need to create a sort of binary system that just operates the reload?

Finish Phase 1? -> Yes -> Finish Phase 2? -> No ->:// Continue: Phase 2

You know something like that? Where it registers only the checkpoints of the phases and using spliced animation allows the program to continue you the reload at any point, it would just neglect the phases not needed (I'm being redundant but trying to put it in terms of operation).

CCP is already going to have to make a ton of reload animations for the new weapons, so along with the building of those reloads, they could just throw a few splices and add some more variables to the already binary system of reloading and bam, progressive reload.

Right now, our reload is cyclic.

We begin to reload but then do something like throw a grenade, sprint, or jump, and we have to restart the whole thing again.

Progressive reload is based on the progress made during reload. This would allow us to complete certain phases of reload without resetting. So we could take out the mag, sprint, load the new mag, jump, and set the hammer. It seems unreasonable that when I sprint after loading a new mag, I take that magazine out. It's perfectly fine yo! Don't take it out you just put it in!