No clear description if how to actually use it.

No instructions on how to calculate users rating. We can't put anyone on a match with a grand master randomly!

No tag or identifier to distinguish each game from other games. By doing this we won't need to send the whole PGN back an forth I believe.

And a lot of stuff like tournaments, puzzles and votes chess is missing that can be defined.

We can define a profile field for user to put their FIDE rating/title with propf.