This comes up again and again. Just tell me who will be the people who will reliably manage which plugins are compatible and up-to-date?
Here's the thing: you go ahead and assemble a team that will reguarly test plugins versus different DokuWiki versions and will go ahead and update the info in the plugin pages accordingly. Once I see this team is working realiably, I will go ahead an make the necessary code changes to rely on this data in the extension manager. We then can talk about testing against different PHP versions, too.
I'm serious. I'd be more than happy to see such thing emerge from the community. Personally I do not have the time or energy to invest myself into this.