Do you think that there is any chance of the major US airlines ever flying non-stop to IST again? That would provide some competition to TK's existing monopoly, and give ST & OW passengers more options.
I personally don't think anytime soon that US carriers would sacrifice their slots from slot-restricted US airports such as JFK and EWR. For the sake of competition, it would be nice to the US3 flying to IST, but it's really difficult at this point.
Also last time when both UA and DL flew from respective NY area airports, TK always did dump the price on their IST-JFK route ( TK didn't fly to EWR at that time ) even during the summer peak season and always offering fares significantly cheaper than UA and DL in both Economy and Business.