Although the directory tree is not formally laid out, there has been a lot of talk about it. The big changes that remember from the discussions are:

• Install multiple versions at the same time
• Tag modules with author name
• Uninstall capabilities

However, the installation targets shouldn't influence your design that much.

Don't limit your discussion to Perlmonks: a lot of other parts of the Perl universe have to work with whatever you come up with. You'll probably also want to work with (not separately) from the current Module::Build folks who have already thought a lot about this stuff.

Good luck :)