I don't really work much on BitStream currently. The idea is already almost half a year old. I've mostly written it up for a friend who wants to implement it. He kept bugging me about it (which I am grateful for). However, for me it was just the predecessor that lead to BitVM.

Next step for BitVM is to complete a toy-implementation of the universal VM-circuit. Then we can compile Rust and C++ to the VM and run stuff like ZKP verifiers. All of that intends to enable bridging BTC to sidechains.

The ZeroSync header chain proof already exists zerosync.org/demo Hopefully, next year we'll complete the first full chain state proof. The good thing here is that it becomes easier over time because proof systems are currently advancing very rapidly.