The relationship with Saunders is so torn that Seattle will probably end up settling for the best possible offer, even if it's just some B- prospect at the end of the offseason.
Seattle could use another good hitter (current projected lineup is probably Cruz RF, Ackley LF, LoMO 1B, Jesus Montero DH; Cruz DH and LF on occasion depending on context).
They could also use quality SP depth. Their top 5 is fine but their #6 and #7 SP don't inspire much confidence (Brandon Maurer and Erasmo Ramirez). With Taijuan Walker (rookie), Roenis Elias (injury scare), and James Paxton (sophomore) in the rotation, someone like JA Happ who they could slot into a swingman role might actually appeal.
I honestly don't think a Happ for Saunders swap is out to lunch.... Saunders is more talented, 4 years younger, and he has an extra year of control, but financial costs are similar and the relationship between Saunders and Seattle is in tatters and the whole world knows it.