I can't see how it would make curation much better. Maybe a little bit, but in the long run it's really difficult task to reward right users at the right time because this is, after all, a decentralized system.
Bigger problem is that it's really hard to find good content from Steemit. For example, I don't care about photography, traveling or food, so while many posts in those categories might be high quality for those who care about them, they are pretty much just noise for me. "Good content" is not good for everybody, only a small subset of users. Most of the posts in trending are not interesting to me. That's why I don't see much benefits of focusing on curation. Some good writers might get a few bucks more, but that's about it.
I want people to have financial incentives for long term. Having to commit for the long term success of the platform makes people think more how they act. If users can sell whenever they want, most of them will not be committed to the platform. They don't have skin in the game. When people don't have skin in the game, they tend to act recklessly.
Also think about this. If my proposal is implemented people who want to power up quickly would buy much more STEEM than they need to shorten the power-up period. This will increase demand and take away STEEM from the market.