You never know for sure how this is going to work out. I will give you one example where it wasn't beneficial for a US carrier.
USAir in early 1990's was hurting and British Airways stepped in with some cash to help USAir avoid bankruptcy. They codeshared on flights in and out of the USAir hubs (PIT, PHL, CLT). However, listening to Steven Wolf at a roadshow soon after he came to USAir, he stated that he would end the USAir/British Airways codeshare quickly since British Airways was getting all the benefit (due to the revenue sharing provisions tied to the help USAir had received earlier).
The point is, wait until all the details are out before deciding whether or not this is truly in Jetblue's best interest or Jetblue is getting robbed by a better financially positioned company.
Good point. According to Dave Barger, details should be out in the next few days. We'll see...