I agree in principle that absorbing the best from the ecosystem is good. However, anything pulled into core should have a long lifetime and be considered part of the API. This deserves careful consideration, and plugins work really well until it is clear there is a reason to pull something in.

Not to talk about the other side of the holy war too much, but one of the things I appreciate about GNU ELPA is it's treated as part of the Emacs distribution and needs to follow all the rules of Emacs proper as a result.