(being like that for like 3 minutes now, after doing undo in weight painting few steps)
if it would at least use my pc resources to do undo… but the program just freezes.
I’m sure there’s a lot to do etc.
I respect that.
But program becoming unresponsive after every “undo”… is there any foreseeable deadline for it to change?
It’s definitely one of the big problems in Blender and it’s on the developer’s radar, so expect improvements in 2.8x versions, I think (always take plans with a grain of salt!). However you can be sure many users have reported this and they are aware of it. It’s probably a big project to undertake a rewrite of the undo system, so it’s not going to happen right now for the 2.80 release.
Also check this (see the links I provided there):