I'm the OP and I'm crying because I'm working on apps that don't have backend so that your data is yours and never leave your computer. This is now impossible for WebKit users.
Sorry if I sound rude, but my conclusion from your article is that the problem here is you don't want to assume the costs and resources needed to build a backend and blame Apple.
Please read the HTML/Web Storage standard [0] and try to find where Apple is not honouring it.
Even before this move by Apple, you should already had to consider localStorage to be subjected to being wiped by actors not in your control.
On top of that, localStorage privacy concerns were also in the standard. See section 11.4.1 [1].
Nevertheless, I reckon Webkit should expose the option to the user.
I feel your pain, I really do, but I can't see how Apple made PWAs impossible.