Will the lack of privacy on Bitcoin enable state co-option?

BIP 300 has nothing to do with privacy, sure you can make privacy focused sidechains, but we already have liquid and no one uses it.

Will the declining revenue for miners mean bitcoin transactions take weeks to settle, forcing users onto other chains?

This makes no sense, the difficulty adjustment exists

Will the scarcity of bockspace on Bitcoin force most users to rely on a custodian?

If this is the scare, something like coinpools is a much better approach. It actually works on solving the problem rather than just creating another blockchain.