[moe]

But I don't think it's rubygems' role to fix what rvm/rbenv fix

Well, it all sticks together. I would say ruby-build should be retained as an external tool to conveniently fetch and install ruby versions.

However, we should very much replace the god awful environment magic that rbenv/rvm perform with native ruby/rubygems support for version/project-scope gemsets.

Rbenv is a well designed crutch - but still a crutch.

In an ideal world you'd checkout a ruby project, point any recent ruby-binary at its Gemfile, and it would download/install not only the required gems, but if necessary also the required Ruby version, as specified by the Gemfile.

It would store everything in './.ruby', which could optionally be backed by a common shared directory (~/.ruby) for space efficiency.