I like the idea, but I think 4% might be a bit too low.

You said your idea was 1% per week so for 4 weeks 4%.

My idea as a suggestion would be to raise 1% for every week.
so first week is 1%, 2nd week is 2% . . . and so on.
So then for a 4 week reduction, it would cost 1%+2%+3%+4% = 10%
This could also allow to maybe add an option where you can do less than 100% time reduction unstaking, meaning for example you burn 3% and get 50% instantly, but still need to wait 2 weeks for the extra 50% or you burn 1% and get 25% instantly, but need to wait 3 weeks for the extra 75%.

Just my idea on how to improve this proposal potentially.

For now I will still vote Yes for this proposal as I like the freedom it would bring to people regarding their SPS holdings and also a nice SPS Burning mechanism.