I doubt Foley is replacing Don West seeing as one of the reasons Foley is upset with WWE is because of being on the broadcast team.
I would call TNA a rival, however I don't think Foley will be good for TNA in the long run seeing TNA's history of signing big name stars. I mean lets look at it. I mean who have been the major focuses for the last 2 years? Angle, Sting & Christian. Former WWE and or Legendary guys. Booker is the first big name star to come to TNA not to squash the home grown talent. (Samoa Joe) thats definatly a good sign, but take a guy like AJ Styles, who used to be the main event star, then has gone from goofy lacky of Christian & Angle and now were suposed to take him seriously as a major main event Face again? I've had a hard time buying it cause I still see the guy who wouldn't leave his bedroom while he tried to decide between Angle & Christian. And if Foley comes in, and if they actually have him compete, you know its going to be a main event spot. And with everything centering around Jarrett & Sting, is AJ really going to be a main event player? Are we really going to believe that AJ has a shot at being the World Champion again? I don't.
Agreed, Foley always hated the idea of be on commentary. Which is one reason he didn't do it for long cause he didn't like it. Which is why he was gunna get in the middle of the Edge/Taker feud but i guess that isn't gunna happen now seeing how Foley is off Smackdown and Tazz is back on (side note: Grisham and Striker suck on ECW)