Making this a requirement is not only more inclusive, it is also much more practical, as it eliminates confusion about how many of each gender are currently on the line for each team. It ensures gender match-ups are correct, ensures gender pulls are correct and removes any cases of mistaking fmps for mmps and vice versa.
Perhaps this signal could even replace, or at least accompany, the raised hand/raised disc as a symbol of readiness that is currently required before the pull?
The only problem I have run into with this so far is that it has often created confusion when players ask for which gender majority is currently correct. I think this is due to people not being used to this concept and a lack of communication and tracking of ABBA by the teams, it would however be good to emphasize that the current gender majority should be shown on the sideline and teams must make an effort to keep track efficiently – i.e. reiterating what the current gender majority is at half time with the other team.