I like snowflake's suggestion the best. The liquid STEEM holding of a certain account will "mature" to voting influence after 7 days.
@leesunmoo suggested similar but more innovative one. When power-up it takes 7 days from STEEM to SP (slow power-up), and can be cancelled if they want during the 7-days. Instead, power down can be done immediately (instant power-down).
That was my suggestion too, but I prefer snowflake's idea because it does exactly the same thing with the added benefit of simplifying the wallet. Instead of slow power-up it can just be STEEM that matures after 7 days to offer influence. It is of course liquid at all times, so you can transfer it immediately etc.
So don't need a second Steem Power component that needs powering up or down, even if it's instant. Just have STEEM - gains influence after 7 days.