What I don't like about BUIP143 is that some BU devs want it to give them "carte blanche" to do a soft-fork against donation addresses.
I'm not at all sure that's needed, or a prudent countermeasure.
My thoughts
1/
Agreed on both main points you made. Blacklisting would be near impossible to implement *and* it introduces a new validation criteria as IFP proposal would have had.