I'm pretty sure they won't announce that they will start flying from and to Lisbon, but I think it's possible that they make some demands, or so. It's public here in Portugal that they interest in it, and that an important person form Ryanair visited LIS two weeks ago.
btw, OPO-Bristol, OPO-LPL and OPO-BHX are back in the summer with two flights per week. These flights will be operated by UK based aircrafts.