Plugin dependencies/migration/versioning support?

I’m wondering about what sort of functionality is being built around
plugin
support for plugin versioning or plugins with migrations, etc. in Rails?
Specifically is it bad form for someone to write a plugin that depends
on
another plugin to function? Should the dependant plugin be wrapped in
the
depender (sorry for making up a word there) plugin’s namespace to
prevent
conflicts? Ideas? Has there been discussion of this on the ruby-core?