I haven't had the time to read all comments, so bear me if this has come up already:
I think the 1.5% interest on steempower are, even without the hyperinflation of the early days, an important vehicle to bind capital in the system. Even if you just lock it in for ~Ø1.5 months. Without the interest you got little to no cause to stay invested in Steem. And if the ~800.000$ got pulled out of the system your proposal would probably do more harm than good. - Anyway, I might be wrong about this. :)
It may be true there are insufficient pre existing incentives to hold steem power, but I feel the additional incentive that a 1.5% yearly interest payment on something with a daily volatility of 5%+ has almost no effect on encouraging anyone to hold more steem power. This is almost certainly not worth the now $1m a year or so, which honestly, can probably be better spent in any other way but this