Wouldn't it be better to just change the definition of community in the
RPSL dictionary so that a community of <digit>+ ":" <digit>+ ":"
<digit>+ is valid and then have the tools either barf if they don't
understand or do "the right thing"? That would seem more consistent with
the current scheme where a community can either be an integer or
<digit>+ ":" <digit>+.

I assume a router that can deal with large communities will accept
standard ones in the same clauses if someone wants to do that for local
use only communities.