In case it wasn't clear, I'm not suggesting to any app or project what they should do, I'm only suggesting adding asking about burning to the evaluation framework/checklist. If an app answers that it won't be doing any burning but will be contributing to the Steem ecosystem in other ways, that may be perfectly okay. But if other apps do find that their economics support burning, that is potentially very positive for Steem, and something that ought to be considered in this evaluation process.

I don't think your suggestion will work entirely because it creates a permanently-powerful account which can (and likely will) then be resold once the app no longer needs it (if only in liquidation after the app fails or decides to pivot and stop using Steem), ultimately competing for value with with STEEM. That being said there is potentially still some value in permanent or longer-term vesting (just as there is already some value in powering up, despite that power down doesn't take very long).