[bza]

The current policy (as enunciated by Stefan Monnier, who took over as maintainer from RMS a few years ago) is for new packages to be added to the package archive unless there's a very strong argument for their providing core functionality. (Packages that already ship with Emacs are unlikely to be removed from the core, though.)

[technomancy]

I've heard it's actually being considered to move org-mode and eshell into packages, provided the release process can be ammended to generate releases which include packages by default.