With the new curation rewards in place this seems like an even better idea than before.
I also propose this change as well, only charging the voting power delta for new votes.
I support this, although I wonder how much of a technical challenge it would add to figure out the difference rather than just replacing the vote and charging VP as normal.
Not much was mentioned about changing votes to less weight, but obviously if that were to happen no VP should be refunded.
I specifically did mention this in the 10%->5% example but no case VP will be refunded.