I don't agree that the hard limit is the only way to promote scarcity.  Bear in mind, no matter how we do this, the scarcity is still artificial.  If we don't do it right with a hard fork, we're stuck with it.  If we increase the hard limit to a high predicted future limit, and use soft limits and/or other block verification rules to impose scarcity on transaction processing, most of the miners & pools will abide by the soft rules even when commenting out those rules is provablely in their own economic interests.  Reputation matters here, even moreso than it does in the "real" business world.