So would be like a modular add on to the core everyone runs? Seems interesting if so. Everyone could have their own 'version' of bitcoin but be compliant at the base layer. Or have I totally got that wrong?!
I’ve been trying to help nostr:npub1nevsewvjqhrsmpfcpdqw6v3e9f6z8w9sq0yt8kpndk2cumw8g6hs5mjmve. They have built a GUI program that lets you install an upgraded signet version of Bitcoin Core with BIP300. There are also a few sidechains like Thunder and a privacy focused zcash fork.
Paul Sztorc is currently building CUSF, which stands for Core-Untouched Soft Fork. It will allow miners and users to choose future soft forks in an organized manner.
The cypherpunk vision for Bitcoin is coming soon
Discussion
I don’t want to misrepresent CUSF, but this is the last solid thing Paul has written about it. There is code on LayerTwoLabs' GitHub
https://twitter.com/truthcoin/status/1743073625328992679?s=46&t=KKPpg4jlAEfn5NMRsS08uQ