[noggin]

That doesn't sound too good in overall, tho' just far is has could go since. I don't know what was "the near to perfect" development time for LE with the Pi3, but relatively we may could correlate to the case of Pi4, to get some timestamp predictions. ?  

Not really a good comparison as in video terms the Pi 3 was the same as the Pi Zero, 1 and 2 series - they all have the same VPU/GPU. The Pi 4B was the first model with a new VPU/GPU (and the h.265/HEVC block is separate to the legacy VPU that handles h.264/AVC decode and encode I believe)

The lack of VC1, and MPEG2 hardware support is a real fail IMO, specially if you consider the hint, that the Pi4 has a somewhat insufficient factory cooling solution -also- for demanding video processing. Also not sure, that how much the software level encoding could negatively effect the PQ quality, compared to the HW level.

AIUI MPEG2 software decode on the Pi 4B isn't a major issue - it's a pretty straightforward codec to software decode with a CPU as powerful as the Pi 4B's - though as you say compute=heat. I wouldn't expect software or hardware decode to differ significantly in quality terms if they both implement the codec correctly. (Encoding is a different matter as you have lots of options - and it's possible for encoder quality to vary hugely)

VC-1 is less straightforward - that's the same generation as AVC/h.264 - and I don't know who well that software decodes (and deinterlaces if the source is VC-1 interlaced). I don't have that much VC-1 content on Blu-ray so it's not a huge issue for me personally.

Proper 3D MVC in "true" FHD is still a must (from my perspective), so I will just hope the best, as for any other listed expectations here.

Yep - it's an increasingly niche requirement I guess - but I know it means a lot to some people. AIUI the hardware is still capable - but I don't know how up the Pi Foundation/Kodi dev list it is.