This is a very interesting idea. It would be worth digging into it a bit on other aspects that have not been addressed.
Examples:
- the need for RC. With a slow power-up, it is impossible to fill them quickly other than by obtaining a delegation from another account.
- network stability/security if a whale does an instant power-down (voluntary or by mistake) and reshuffle witnesses.
Very good points.
RCs system could remain as it is, with full capacity given instantly. I don't see why not.
For the error powerdown, we could make it 1 to 3 days, that would would give enough time for someone to realize the mistake. About the witness shuffling, we currently have the same issue when a whale powers up huge amounts, so it shouldn't be a big problem.
It is unlikely that a whale powers 100% of its stake down if it can powerdown 25% of its HP in one day.