Given the architecture is heavily dependent on DI (dependency injection), I don't think its even "possible". (The Autofac version must match). And even if that was not the case, it would be more than just "marking their libraries as forward compatible"; you'd also have to include all your version dependent dlls in your plugin folder)
Yes I understand. That is the problem. There shouldn't be any DI for plugins. Its a plugin, stand alone, that is should communicate through an interface. Currently, the architecture is not really a plugin design, its more like a load on demand library (with dependencies).
Having plugins truely stand alone will also open up the market place for developers to reach a broader audience.
Think about this, woocommerce core has a degree of backward compatibility. And who is more important? Your customer base or the current architecture?