Agree with this. A concern with two "tiers" for SP is that current 2 year locks have entered the arrangement with the understanding that their interest rate is crazy high. To change the game is a pretty tough pill to swallow (and will be greatly affected by market conditions, for good or ill).
As for the shorter time period, there will naturally be a dump. You can count on it. But that's what markets do, and this overall plan would free up the market more, distributing Steem to more hands and, IMO, adding greater long-term stability.