I agree Liquid isn't open or permissionless enough, i never used Liquid either. Alternatively, you could check Rootstock (
https://www.rsk.co/) which have smart contract capability. It's less promoted than Liquid, but AFAIK it's more open and use merged mining on Bitcoin network.
I'll note that. I knew this won't be easy by any means, but it seems horribly hard. I'll need to research a lot more than I thought, but I still like the idea. I need to talk to some friends. Thanks for some first impressions!