If the rumours are true... can we expect a new Pokemon game to celebrate the launch of the NX and the Pokemon 20th anniversary. After all, it's a handheld and how do you sell a handheld? 

You did e.e XD I'm not confident that they will. Pokemon, to my knowledge, tends to wait at least 2 years before releasing on a new handheld

I've been guessing this for a while now. By the time I'm expecting NX's release (November) it will have been more than 3 years since X&Y, Pokemon generations usually last anywhere from 2.5-4 years, as well as it being the 20th anniversary this year, I can definitely see Gen VII coming at NX's launch if Nintendo want it to sell huge numbers. It would also allow for a B/W situation where we can get two generations on the same console and thereby sell even more. It makes sense to me, even if Pokemon has not traditionally been a launch title.

The only way that would happen is if NX released next year, as the 6th gen of Pokemon still needs it's third game. Pokemon Z will likely be the anniversary game. Yeah a new gen for the anniversary would be cooler, but I don't think they're gonna change their conventions just cause an arbitrary amount of time has passed since the first game.

If the NX is a handheld and is releasing in 2016, then it would make sense..

Hmm, that certainly seems possible. If it's not gen 7, a 3rd version title game does seem possible. It's been awhile since we got X and Y. So I think it is more likely we could see a new pokemon on the NX.

hmmm
id bet on the safe.
pokemon Z on 3DS.

On NX Id bet on something new. a game that could interact directly with pokemon go on your smartphone, and give you more options than for those who only have go on their smartdevices.

Maybe something relates to Pokemon Go?
Maybe like you can connect your smartphone to the NX to access extra content for the pokemons you captured and other shit.

Maybe another Pokemon Spin-off? I would love a Pokemon Warriors game!!!!

No. Everyone knows the real way you sell a new Nintendo handheld is with a Tetris pack-in.