The proposed "tax" to powerup is a bad idea. We want to encourage people to stake hive not the opposite. Same goes for the "tax" on claiming rewards. Think about it, 75% of the rewards are in the form of staked hive (already locked up) and the other 25% is comprised of HBD not Hive.
I have never powered down in my almost 5 years on the network (except when I was doing it to pay for a recurring delegation that I was getting from blocktrades back in 2018). But, if a change like this goes into effect then that would signal to me that it's time to sell my Hive position (with regrets).
I am ok with charging a fee (tax is a "bad" word) for instant powerdowns but the other 2 components of your proposal are a dealbreaker.
There are other better ways of removing Hive from circulation than adding friction to the system like for instance adding use cases that burn it. Or increasing the interest payed on the savings account that (combined with the ability to convert Hive to HBD) could potentially lockup millions of coins and turn the blockchain into a defacto DEFI ecosystem.
Introducing a tax to power up and to claim rewards automatically reduces the APR making Hive less attractive to investors. Combine that with the fact that the inflation rate is being reduced until it eventually goes below 1% and you get a recipe for an economic disaster for Hive.