I've been working on a local-first web app, and ran into some of the same issues. Good to learn about these other pain points..
All of these make the so-called "persistent" local storage unreliable and impractical. I don't understand how browser vendors expect people to use such a feature where the data can be deleted at any time, where neither the developer nor the user has any control over how that happens.
I don't think there is a real plan, I think it's just the current state of the power struggle between two competing factions. Some browser devs prioritize web apps being as good as native apps. And some browser devs prioritize not causing problems for users (such as using too many resources). Seems like sometimes one faction sneaks something past the other to advance their cause a bit, and in total the result is incoherent.
All of these make the so-called "persistent" local storage unreliable and impractical. I don't understand how browser vendors expect people to use such a feature where the data can be deleted at any time, where neither the developer nor the user has any control over how that happens.