I agree, it's still possible if the top 20 agree on doing it. It then would be up to stakeholders to remove them from consensus. It's more likely to happen on steem though. I am wondering how long would it take for the internal RC market to adjust to the increased demand.

Technically the blockchain would not stop with "spam" operations it would just be more expensive to transact and witness nodes would have an increased cost over time and replay time will get bigger with blocks filled to the max.

I think that right now it's cheaper to transact on steem because the effective SP being used is about half that of hive (less transactions = lower RC cost) so it's easier to "spam" it.