Well, here's the thing: they're saying the game is "free to play up to Level 50". Now, right now the cap is at level 50, which means that it will be absolutely free to play through the entire storyline of the game, all class quests, all of which are PVE only.
So all PVE elements will still be playable the entire way through the game. Granted, items bought with Cartel Coins might make it easier, but since there's no competition between players in PVE, then there's no risk of one player being better than others because he pays.
Where this might be an issue is PVP. A player with special gear purchased with Cartel Coins might have a distinct advantage in PVP combat areas. But Warzones are team-based, so one should expect a nice balance of paying and non-paying players on either side of a Huttball, Alderaan Civil War, Novare Coast, or Voidstar level, and exclusively paying players on the new Warzone (whose name I don't remember, that takes place on Asation). Where it could get really complicated is Ilum, where it's a lot of open-world PVP. But this takes place at Level 50, and they're saying that it will be free to play to Level 50. One could interpret that as "You can get to the end-game content on a non-paying account. And while you can access most end-game content, you may not be able to compete with others there."
But a mechanism like this should, in theory, have no negative effects on PVE content, which is the vast majority of the game.
It was the year of fire… the year of destruction… the year we took back what was ours.
It was the year of rebirth… the year of great sadness… the year of pain… and the year of joy.
It was a new age. It was the end of history. It was the year everything changed.
The year is 2261.
The place: Babylon 5.