Van Kane has a great post on his blog, Future Planetary Exploration, on the potential for future New Frontiers-class (or Discovery-class) missions to Io. This is the first in a series of posts on mission concepts and the likelihood of an Io mission. Definitely worth checking out.
I will try to post more on the solar paneled Io mission concept later today.
Link: Io Missions: Part One [futureplanets.blogspot.com]