An Io mission is certainly ambitious and fascinating. But from what I know of Io and Jupiter's high-energy exchange, you'd have to build your probe incredibly, heavily, expensively shielded and hardened for it to survive.
Announcement coming at 4pm ET Thursday for NASA's Discovery Program down-select.
I think that if somebody dug around, they could probably come up with a list of maybe 15 of the ~20 proposals.
I would prefer the Triton mission. We already have quite some data from Venus and Io. Additionally there is Juno cruising inside the Jupiter system and more upcoming missions to the Jupiter system. Neptune and Triton are barely known.
The Triton mission sound very cool, and I would be tremendously pleased both to get out to Neptune and to possibly confirm another ocean world, but if it is just a single flyby, I really hope there is more planned before and after the main event.
I posted this news elsewhere and in the feedback the poor old Venus missions were always listed last. Guess they just can’t compete with what’s seen as the more exotic targets such as Io & Triton.