I feel at the end of the day, it's a lot about whether or not a player is good and can turn the tides / make a team too strong more than 'what a certain player main module is'. People who have been playing two or three modules at the same time exist and just because they may have had a stronger inclination for a certain module at a given time doesn't mean they are not 'committed' to the other(s) module(s) they are playing. For instance, I am one, I have been involved within the native community for years, recently as a player too, but because I'm neither a good NW or Native player, it's not an issue what's considered to be my 'main' module, because would I play, my presence wouldn't make a team significantly stronger.
I fully understand why you are doing that though, I do not criticize the idea, rather I salute it cause I know it's here to make sure the tournament is 'fair' for everyone and not filled with native 'mercs'. So long as you either are very light on the rule (by considering people like you and Lapache are also full NW players at this point) or very strong (you, LP, Maxime and potential others are all primary native players and should be treated as such in this tournament), I reckon it should both work. But dealing with situations on a case per case may result in a lot of bias which I'm sure you want to avoid.
Either way, that was primarily an answer to LP, good luck to hosting this tournament Python & Marxeil and thanks to Gibby for assisting them.