Are there any examples of sidechains which target a block time much longer than bitcoin? Could a sidechain be made "slow enough" such that the size of a proof (SPV proof?) for it could actually fit into and be verified by a mainchain bitcoin transaction with the currently-in-effect mainchain protocol rules?
I'm interested in learning more about how a sidechain with a targeted time between blocks of, say, 1 week, might work and/or if such a chain, if it existed, could be useful.
I'm specifically interested in proof-of-work sidechains that do not rely on any sort of federation (as such, Liquid and RSK would not meet this criteria at the moment, but I'm unaware of any other current examples of bitcoin sidechains), and I'm most interested in "slow sidechains," if any exist.