In general I thin the libretro team is doing a fantastic job. Finding the balance between front end development and core development is hard.
I agree that dolphin, ppsspp are pretty outdated. But maintaining all cores is hard work. In my job I have to maintain hardware revisions and different software brachnes for each revision depending on the region where the hardware is used. It is a nightmare. The key was to reduce the hardware revisions to a bare minimum and keep the software branches small as possible. So I can imagine what kind of work that is with regard to the cores.
Maybe the solution is to focus on main cores for each gaming hardware. Means for nes its mesen, for snes its snes9x for n64 its mupen-nx etc So the ressources can be used more efficient. But as said I think the team is already doing a great job.
With regard to standalone va libretro. I would also like to switch completely to libretro but there are some features which are currently not possible in libretro. For example the movement assignment of the wiimote in dolphin, or the mapping of touchscreen buttons in citra.