In reply to alex.

Well as a User and a Dev that's not workable at all.
I can just imagine ringing my clients to explain that WordPress 5.0 is not backwards compatible and they will have to buy/get a new theme, all new plugins to replace the ones they use (assuming a plugin actually exists for 5.0 to do the same job) and of course the some 20 hours of billing while I rebuild there site on the new platform.
A much better solution is to improve the system for changing version numbers, it's a reasonably simple exercise and as has already been stated it would make the Dev's lives a bit simpler so they would actually do the update to the version number. I understand the frustration as It drives me rather nuts when something I wrote for free then requires a dog and whistle show to update a version number.
I also totally support the idea of a dead plugin bin were Dev's can adopt an old plugin and make it viable again.