I'd love this too, but rather than selecting which files to open, I'd like to open all files that match a regex or wildcard.

For example

ctrl+p

foo.*\.rb

=> opens foo.rb, foo_spec.rb, foo_steps.rb

I'm not sure whether I'd prefer regex here, or something similar to shell globs; probably the latter, thinking about it.  Regex is a bit jarringly heavyweight for a simple operation, with its escaping characters etc...