I think the Grass/Fire/Water thing is getting slightly stale myself, and could use some new creativity... Personally, I think it would be really cool if they kept the same Grass/Fire/Water triangle, but just put a new spin on it....
Like, instead of having 3 starters, just have one that evolves into several different pokemon (like Eevee) depending on some factor... Make it like Wurple, where the player doesn't know what it'll evolve into, or maybe like Tyrogue... Either way, I think it'd be a cool idea for a starter.
...But that's just my opinion.. I won't be surprised if no one agrees with me...
True, things that aren't broken shouldn't be fixed, but that doesn't mean that they can't be innovated/improved on every now and then. Just because something is a "tradition" doesn't mean that breaking it will be inevitably bad. There is always a possibility that breaking a tradition will create a new one that's even better. But of course, yeah, it could just be bad.
That being said, GameFreak will probably just stick to the old tried-and-true method concerning pokemon starters. Simply because it's tried-and-true.