I see a few problems with those proposal

1) You are proposing to fork the blockchain without consensus. This in itself is a problem, we don't want to fork without consensus (even with a soft fork) because there is still the possibility of the old chain surviving, and that can lead to some major problems.

2) Your generalized soft fork idea breaks one of the basic principles of Bitcoin, storing all of the transaction history in the blockchain. It is not possible to know what the transaction data is if you use your idea to transform blocks under new rules to blocks under old rules. It isn't backwards compatible so it isn't a soft fork. If I ran a client with the old rules, then I would not be able to know what the transactions were in that block without having to download the fork. That is completely pointless.