What does HackerNews think of picolove?

There are more:

https://github.com/picolove/picolove (Love2D)

https://pixelvision8.github.io/Website/ (Lua)

https://hallucino.itch.io/px8 (Lua/Python)

https://liko-12.github.io/ (Lua)

https://github.com/antirez/load81 (Lua)

https://wasm4.org/ (WASM)

You can get that to some extent: https://github.com/picolove/picolove

If you'd like the platform to be more open, it's pretty easy to do something about it, just contribute missing bits to existing open source implementations like https://github.com/picolove/picolove. The overall system is pretty simple, so completing a decent open emulator should be be doable in a reasonable time frame.

Personally, I'd both like to see and open-source way to play back pico-8 cartridges and lexaloffle continuing to be financially rewarded for building a pretty cool (and cheap!) platform, so I hope the graphics and sound editors won't be included in free clones anytime soon.