Greg's other concern seems to be about fees.
While that's important, I don't think it should be a major consideration this early
when coinbase subsidies will likely be greater than fees for
at least a decade, and so not a reason to forestall an increase.
Fees concern is well addressed in
BIP 1xx. Greg is simply doing whatever it takes to honor the 21m he has taken for BlockStream, i.e. choking the network, so that BlockStream can bloom.