There was a big rewrite in 2019? I haven't been following these things. (I think byuu left, and then came back, and then decided to leave again?)
That was the year when BSNES got a good GUI more along the lines of Snes9x, a huge speedup (to almost Snes9x levels) that sacrificed nothing for just playing in the end, which even then was optional (when fast modes are turned off, it's as accurate as Higan), the ability to emulate flawed emulators, and Sameboy integration for super game boy. Then out of nowhere there was run ahead and HD Mode 7. After all that it was declared over 100% complete and Byuu/Near put the emulator up to complete FOSS without him as owner. And to be fair, all it really needs anymore is general maintance and the ability to work in new OSes. There's also the HD branch with widescreen and such.
I would expect that someone would have tried to replicate the ZSNES GUI just for kicks.
ZMZ is still kicking actually, since it uses Libretro cores of bsnes it's pretty much always stays relevant. IIRC there's also a neat Raspberry Pi thing out there that basically turns it into a better SNES classic, and just packs in and updates all the SNES cores. Don't remember the name though.