We already track and show the dates of nodes. Perl 5 solutions will still be useful in Perl 6. I just don't see a problem here beyond the usual problems that already exist.

Perl 5 solutions will still be useful in Perl 6.

Maybe not. Module and algorithm advice will remain valid, but many people come looking for code snippets. Very basic things like the syntax will change in Perl 6. The elder monks will have no problem reading old and new code and telling them apart, but beginners will be confused if some nodes write  $a[3] and others  @a[3]. So it has to be made clear what version the node is talking about.

Of course, since Perl 6 is not exactly imminent, neither is this problem. (Things may be different with Parrot which is maturing faster).

You're completely right about the need to differentiate which version of the language particular code is in...especially in the long transition period. Perhaps <code5>...</code5> and <code6>...</code6> tags (whose contents are displayed in different fonts) might be a good starting point.

And if these were used consistently then it would be a SMOP to have the monastery itself append [Perl 5] or [Perl 6] (or both) to node titles, depending on what kind of tags the node contains.

Oh, and Perl 6 is quite a bit more imminent than you think: our goal is to have a beta out this year.