Right now you can only have one virtual path per directory level. vimfan on this thread suggests a use case for having multiple variables per path part:
We're constrained by what are valid characters in a filesystem name: we certainly can't support arbitrary regular expressions as virtual path names. Can we come up with something else here?
Right now the answer is: 'use a greedy simplate file'. What constraints of 'valid characters in a filesystem' are a problem? They can all be escaped with \s, I think. Not that I'm really in favor of this... "now you have two problems", as jwz says. If we really want to allow regexs, I'd suggest something simpler than full-on python 're' support - maybe one of the re2 variants like https://pypi.python.org/pypi/re2/ . Globs are so simple they're not worth doing (any use I can think of for them might as well just be a set of nested dirs), but an re2-based dispatcher could be done if it was really deemed useful.
Haven't gotten any further interest from the original poster or others. Let's close for now and reopen if/when there is further demand.