I would love to see a shared Composer-like resource for WordPress assets. A really common would would be Stripe - imagine being able to use either stripe-php-1.18.0 if you want to provide 5.2 support, or the latest if not - or simply just version locking your dependencies :)

I think the the major reason that this should be a priority for the Core team is how much potential it adds to the ecosystem.

It does seem unlikely that it will even be a possibility until the minimum version of PHP gets bumped though :(