I've now tested the new addon version 28.7 to see which bugs have been fixed. This is mainly focused on the bugs that I've experienced myself before and which I reported. Here's the summary ...
FIXED
*) Object motion blur works now.
*) Switching kernels preserves settings.
*) Server load is low now when Blender is idle/off.
*) Connecting nodes from the World Output node refreshes the preview.
*) Appending Gradient nodes works now. But make sure to save the parent scene with the new addon.
NOT FIXED
*) Activating Render Preview (especially with many objects in the scene) is incredibly slow - almost unbearable. In a standard scene it's about 800% slower than 27.16. This affects everything down the line (switching to Edit Mode, isolating objects, ...)
*) Overall Render Preview still is noticeably slower than 27.16.
*) Switching workspaces doesn't update view mode icons.
*) Canceling renderings doesn't work when denoising is enabled.
*) ACES checkbox in the preview panel doesn't work.
*) Activating render border crashes Blender. But this was listed as not working in the release nodes.
*) OCIO updating when switching in and out of camera isn't working.
*) Starting Blender when Octane server isn't running takes quite long.
*) Bump map scaling is still wonky when comparing the Bump Height settings vs. increasing strength via a multiplier.
*) Not a bug, but menu entries still aren't capitalized. A "nice to have" but the rest is much more important.
That's the first feedback. So still a long way to go. But being able to use it in Blender 4 is a good move.
Blender 4, addon version 28.7, RTX 3060, Windows 10.