Maybe, but it wouldn't be impossible to rebuild plugins around Composer and PSR standards. And doing so would make them better organized, and make it easier to manage third party dependencies. If you were going to build Wordpress from scratch, today, that's probably what you would do - just make plugins a special case of Composer dependencies.
The only question is, whether you would still have as robust an ecosystem with a more restrictive framework? Probably not, but the quality of plugins would probably be higher.
I filed a core bug report once. Long to short, if I passed (I think it was) false to a core function, I got very unexpected results. The dev that replied to me said, "Well then don't do that." Huh?
The idea that the function should check, that it should be aware that humans (and their code) make unexpected mistakes, was completely foreign to her / him. I lost a lot of faith that day. I lose a bit more every time I go poking around in core code. I'm no Super DevMan. So when __I__ see bad patterns you know something is wrong.
p.s. Fwiw, even the lead dog (i.e., Automattic) has some nasty code habits. Simply dumbfounding.
But those are The Right __and__ The Wrong.
For example, adding Composer to the WP "stack" makes sense. But now you've eliminated 90% (?) of the WP "developers."
That is, in the Universe of WordPress Composer is more friction, not less (i.e., ease of use).
Long to short, for better or worse, WP is Justin Bieber. It will never be Radiohead.