It will be interesting to see what effect SWToR has on Rift. If Rift had gone much more down the Daoc PvP line I would think that SWToR wouldnt effect it as they would be different styles of MMO, aimed at different types of players.
However as Rift hasnt really gone much into the PvP side of things, from what I've read the actual game mechanics of SWToR and Rift are , at their core, pretty similar (both kind of following the WoW style of mechanics) and as such I think they might well be direct rivals to each other (even with the fantasy/sci-fi difference).
Will be interesting to see how Rift adjusts to the release of SWToR, and then later on it will be interesting to see how Rift AND SWToR adjusts to the release of Guild Wars 2 (although given what I have read of the mechanics of GW2, it might not be a direct competitor as its a different style of MMO)