This RFC should change the semantics of the GASLIMIT EVM opcode too. It should return the gas limit of a single transaction and not of a whole block.
In the context of a smart contract running inside a transaction GASLIMIT is only useful for assessing how much work can be done in one go, in a single transaction. If work must be done over 2 transactions, it doesn’t matter if the other transaction is executed in the same block or in the block that will be mined 12 seconds later. For a smart contract the gas capacity of a block is a meaningless number.
I’m late to the party, but IMO this is a veto-worthy defect of this RFC. If it’s applied without altering GASLIMIT, it will likely break most contracts using this opcode.