Ethically, this situation has some similarities to the DAO fork. 

There are no similarities.

The DAO fork was against the principles of cryptocurrencies: a change of the ledger done in violation of pre-agreed rules. The whole point of cryptocurrency is to avoid shit like that. (E.g. a central banker changing ledger as he wants.)

Greg's proposal is in line with the principles of cryptocurrencies: PoW-based cryptocurrency can work only if there is a competition between miners, which requires all miners to have equal access to the technology.

The notion that Bitmain is entitled to future profits is completely ridiculous. Every investment has a risk, and doing unusual stuff which boosts your profits is associated with increased risk. Developers just need to make sure all miners are on equal grounds, as that's the whole point of the protocol. If Bitmain loses their profits because of that it's really just Bitmain's problem.