Some similar ideas have been discussed in the context of having "investors class" of SP/VESTS that would incentivize opting out of curation (also something @arhag has discussed/proposed). This particular variant I just came up with.

I don't really have time to get into the question of curation rewards, but some aspects of it are pretty obvious: motivation to buy SP (though as you say, only in large quantities), for those who are good curators, incentive for stakeholders to actively vote and not succumb to voter apathy, etc.