You should stick with perl 5.
You can use perl 5 today much more easily than e.g. pugs, which is definately not a stable platform (albeit lots of fun).
I do suggest you look at, and familiarize yourselves with Perl 6, the pugs project, the synopses, etc, and design something that is easily portable to Perl 6. This is mostly a design issue - Perl 6 has roles, grammars, better support for higher order functions, etc. This means that while some things look equally ugly in Perl 5, one of them might be beautiful and easy to read in Perl 6 - so this could affect your decisions.
Much more important, IMHO, is community involvement and interoperability. If you want this Oak project to work out well, please make sure that:
- You have a publically accessible respository, where people are encouraged to contribute (especially tests and documentation)
- You have an IRC channel and/or mailing list so that people can meet, get help, and group think
- You reuse familiar modules from the CPAN, especially for small mundane tasks, or contribute/replace modules that aren't fitting. Keep things generic!
- Keep things very simple - many CPAN modules are hard to use because of an installation headache. Since Perl is so portable this can actually a pretty tough issue to deal with. This also applies to your interface, but of course you already knew that =)
- Invest some funded hours in the tasks that you are not likely to get volunteers to do, but that are equally important - documentation, high quality tests, etc.
These bits of advice are mostly from watching the success and failure of the Catalyst project.