Why you want to support the old behavior in the new component structure?

If using the new component structure, why should i be forced to have a file joomla40/administrator/components/com_content/Extension/ContentComponent.php that extend MVCComponent and implements RouterServiceInterface?

Before this PR the new component structure was more flexible and all of this was not required. I was able to have a working component having a instance of $component = new MVCComponent in the service provider

If your only concern is not to have your own extension class, then it would be better to introduce a base class in core, similar to the MVCComponent, which components can use. The idea behind this service provider story is that we have one way to access these services.

Before this PR the new component structure was more flexible

Actually the opposite was the case. You had to place a specific file into the root of your component with a specific class name. Otherwise it would not work. If somebody needs the router on a different place, then the same code, to load it, had to be duplicated. Really, we should start getting rid of this magical file and class loading and work with interfaces and standard ways to access services of a component.

Well long story short story i refactored my extensions in order to use this structure. Basically i would prefer a core architecture that doesn't force developers to have a component extension class if needed only for the router service and nothing else. So a base concrete class of MVCComponent that implements BootableExtensionInterface, RouterServiceInterface, etc as your proposal could be a good idea.

I would go instead of with a new class which extends MVCComponent as it is very likely that a component which has a router will also have MVC.

Just for the record, you can also write in your services/provider.php

$component = new class ($container->get(ComponentDispatcherFactoryInterface::class)) extends MVCComponent implements RouterServiceInterface { use RouterServiceTrait; };

Yes correct, an anonymous class there would do the trick as well.

I'm going to close this one. If you want to come up with a new base class, please open a new pr.