In my opinion the whole powering up/down thing should work a little differently. The idea is that if you want to have control over things on the network like witnesses and the reward pool, you need to make some kind of commitment. So that's really what Steem Power is - it's the commitment to stay invested in Steem for a certain period of time.
The problem is that it's not a fixed period of time, it's 13 weeks from when you start to power down. Instead I think that SP should be able to be powered down instantly as long as it's been powered up for at least 13 weeks.
This way, powering up is committing to stay invested in Steem for 13 weeks, and after that you've met your commitment and can power down instantly.
Now some people will complain that that removes the security aspect of being in SP, i.e. if someone steals your keys you have 7 days to react before they can sell anything. But there are other ways to add this same security while still achieving the power down periods that we want.
And lastly, I'm not sure 13 weeks is the right number, and maybe 4 weeks is better, but no matter the number I think the method of powering down that I described above makes a lot more sense than the current system.

This is @yabapmatt's approach. He dropped this comment on my last post and I think it is a great idea.

In addition maybe nobody should have voting rights for the SPS and witnesses until the have stayed powered up >= 13 weeks.