I don’t think ICP is too mature for drastic changes, the crypto space is still quite new, and nobody is making a general purpose computing blockchain other than DFINITY. The only thing close to it is the proposed “stack” using ETH as a consensus layer, another network for computation and another network for data storage.
As for the Bitcoin integration, I don’t care about it personally because IMO DFINITY shouldn’t have given BTC special privileges just because it currently has the biggest MCap out of all the coins, they should’ve just made tools for devs to easily integrate chains into ICP and stayed politically neutral.
Current projects shouldn’t have to redesign their code in any major way, except for having to specify the amount of nodes each of their cannisters would desire to have validate them. The core design of asynchronous communication between cannisters would stay the same.
All in all however I am pretty pessimistic about DFINITYs ability to even consider this as a proposal.