SWTOR all but announced over the weekend that their long rumored "super secret space project (SSSP)" is a new off-rails space dogfighting minigame (see Ootinicast for a detailed summary of the event). This idea is pretty universally popular (see Werit) - does that make expanding the game this far beyond its current scope a good idea?
The big trade-off when adding a major new game feature is the time that the developers weren't able to spend developing something else. When your game already has instanced dungeons for 4-6 players including a tank and a healer, and you go to add instanced content for 3 players with no class restrictions, you are building something that is plausibly of interest to people who are already playing your game.
By contrast, we have EVE Online's decision to expand their space economy game into a First Person Shooter spin-off (that was platform exclusive to the PS3 for no reason that I've ever heard explained by anyone). I haven't heard how this effort has done recently, this idea has always faced a challenge because of how far it strays from both its parent and its new genre. Why would someone looking to play a new FPS want their battles to be dictated and decided by people playing a different space combat game?
SWTOR's project isn't quite that extreme. Space dogfights are a major part of the Star Wars lore and movies, and the game was widely criticized at launch for including an on-rails space combat game rather than a more open system. That said, the current system is also completely optional - I never completed a single space combat mission (I did somehow fail the first one I tried about three times before giving up on the system for good), and it's even access-restricted for non-subscribers.
Thus, the question remains - if you weren't willing to play the game before, why would you want to put up with an MMORPG as a condition of getting your space combat game? If you are a current player but off-rails space combat was an absolute must-have deal-breaker feature, wouldn't you have quit SWTOR by now? More likely, the question of whether this was a good use of Bioware's time will hinge on its ability to extract more revenue from existing players. The sale of cosmetic ship appearances in the cash store gambling packs is an absolute certainty, and it remains to be seen what else they will have to tack on in terms of sales of power and/or access to recoup their investment. I wonder if the system will be as popular when it's more than just a teaser video.