Sorry for resurrecting this old thread - facing the same need as OP and was wondering if his request might be considered.
Dirk, to your point I noticed PyPI, RPM, and DEBs exist these days
For the above packages it seems the authors ostensibly assigned version 0.1 to whatever gyp's latest revision is at the time they author. (haven't looked closely)
Meanwhile the Homebrew maintainers have remained quite adamant over the years about only using upstream tags.
Even if it's mostly meaningless, it seems like it might make things convenient and consistent for downstream to have a tag.
Thanks for considering. Sunk some time into tracking this down and hoping to make future developer's lives, including Keith and Ted's here, easier.
~Patrick