Then "Bandwidth Demand — SP Sites will need to pay for large bandwidth demands by buying and staking STEEM" means that the needed amount of steem will also have to go down?
Suppose it would be a fixed amount (take eg 1000 STEEM). If STEEM price goes up, this would mean a bigger investment to start using SMT which makes it less usable.
And probably it would also mean that it won't be as 'easy' anymore to collect steem for your content / curation.

Though: I think it's clear from my comments that I don't fully grasp yet what this SMT will actually mean ;).