One planet should be enough at launch, with the possibility to add more later on. What is interesting here though, at least in my opinion, is if the plan to implement a day and night side on Arkhona.
It would be amazing if we had that level of consequence to campaign victory, but I'd say it's more likely new planets (or means of adding very different types of battlegrounds) will be in addition to the existing content. Otherwise, that's a lot to be thrown away...
I'd rather have one large planet where the fighting is consolidated. Having multiple planets, while cool, may lead to the players becoming too spread out and people capturing empty bases because there is no one around to defend it.
Oh by multiple planets I mean when one planet is won by whoever, then they move onto the next one, fighting on more than one planet at once is a few centuries ahead .
A change of planet could be feasible if it was an expansion pack type deal, like EC2, thus allowing the playerbase to experience all new scenery/scenarios on a new world..probably with the extra option features typical to expansions, new race/s, new class/es, new weapon/ary etc.. Though their current multi-continental world model will keep us all busy for the forseeable future I'd imagine, that alone allows for terrain and structural variation/updates to keep the experience fresh as the battlefield moves from one continent to the next over time.
At the moment? Apparently not. Earlier on they did mention planet to planet warfare though, and I don't really feel like trawling through dev diary after dev diary (especially when I have work to do). If they do, they do, if they don't, they don't. That's my motto with EC. I just trust that, awesome geeks that they are, the Devs will get it right.