Last year Nobu asked me to propose an API for adding an object to
$LOAD_PATH (instead of a String) that could do the work of finding paths
to load.  The reason was to avoid the pollution of $LOAD_PATH that
RubyGems causes as it activates multiple gems.

I have created a proof-of-concept implementation called fancy_require:

http://github.com/drbrain/fancy_require

specifically:

http://github.com/drbrain/fancy_require/blob/master/lib/fancy_require.rb

The API I propose for the lookup object added to $LOAD_PATH is:

The lookup object pushed onto $LOAD_PATH must respond to #path_for.  The
feature being required (file name) will be passed in by Kernel#require.

The lookup object must return the path to the feature, true, false or nil.

If nil is returned Kernel#require will continue to the next item in the
load path.

If true or false are returned the lookup object handled loading the file
and recording it in $LOADED_FEATURES.  The boolean will be returned as
plain require.

The true/false behavior would allow the lookup object to load features
from a non-file object like a tarball.

I think Ruby should also add a method that would determine if a feature
is in $LOADED_FEATURES.  Maybe Kernel#loaded?(feature).  This is not
strictly necessary.