Maybe try hacking the frustum slice distances via memory editing... an easy way would be setting 0x70CC28 to the lambda value as per the
nVidia paper blockland's shadows are basically copied from, so what the lambda value/split_weight variable would be in updateSplitDist. Higher means splits are shifted towards the camera, lower is farther.
Blockland's slices are already pretty spaced out compared to what you'd see in games like GTAV, but I guess with PCSS its not really a priority to have crispier shadows anyways. See if messing with the slices does anything, otherwise it might be one of those things we have to "deal with" just like in GTAV- any method to nicely blur the lines is likely beyond shader edits or simple hacks. Just one of those things to tweak until it is right, as we all know it's what we sign up for when messing with shaders anyhow :P
Also the fact that a lot of this technology has been around since forever makes one wonder why they didn't deck out the shaders with it when they were released. It looks like the
original thread had some form of softened shadows too... but if their lack of existence tells us anything I'd guess they scrapped the idea because of some visual error/sacrifice. I wonder what!!