We basically have the 7 main PGN tags with an additional GameID tag for the RHP game ID, but there are a few more which might be quite helpful to everyone without adding too much bloat to everyone's PGN archive of their games.
First, set-piece games can be fun, but you need to know the starting position before the moves make sense. How about adding the FEN and Setup tags to include the FEN of the starting position and indicate it is a setup starting position game? These would only be included for set-piece games, as it makes little sense to include otherwise. This can be found in the section 9.7 of the PGN Standard document. It would basically look like this:
[ Setup "1" ]
[ FEN "r3kb1r/ppp1qppp/2n5/3p1b2/3Pn3/3B1N2/PPP1QPPP/RNB2RK1 w kq - 6 9" ]
Sometimes people just don't finish their games and get timed out for whatever reason. That is just past of how things work for tournaments and other events both on the board and at RHP. Using the Termination tag would be helpful to indicate a "time forfeit". If a game ended normally, then there isn't a need for this tag. Section 9.8.1 of the PGN Standard covers this as well as other tag values.
If anyone else archives with ratings to track general performance improvements from study, they might find the WhiteELO/BlackELO or the WhiteRating/BlackRating tags good to have included with the standard 7 tags. Section 9.1.3 of the PGN Standard mentions the creation of rating tags for other rating agencies, but I believe the WhiteRating/BlackRating tags would be more recognized than WhiteRHP/BlackRHP would.
There are quite a few PGN tags which could be used, but they would also add more bloat than benefit quite possibly. The EventDate tag might be one of the few exceptions.
A link to an HTML version of the PGN Standard document is: http://www.yacdb.com/pgn/pgn_lidx.htm , if you are interested in looking up what I saying here. Granted this has probably been mentioned and mentioned and even mentioned, but I thought this suggestion might be very worthy of mentioning.