To get a more precise map of the activity on Io we really need an orbiter there observing the planet on a continuous basis, something that is at this time impossible, not only because no mission is planned but because the hostile radiation environment this close to Jupiter makes the engineering quite challenging. It is this reason why Europa Clipper is not going into orbit around Europa when it arrives there in 2031. Better to orbit Jupiter and only periodically dip into that harsh radiation environment.

Worth noting that one of the finalists in the last NASA Discovery program round was Io Volcano Observer (IVO), an APL/U. of Arizona proposal to study Io; it proposed adopting a similar flight profile as Europa Clipper, inserting into an inclined orbit around Jupiter, encountering Io nine times over four years, with IVO approaching Io from over its north polar region, making its closest approach to Io near its equator at an altitude between 200 and 500 kilometers, and leave Io over its south polar region. This would have minimized its exposure to the most intense parts of Jupiter’s electromagnetic field.

IVO wasn’t chosen, alas; but I think the team hopes to revise and propose it again if Discovery ever gets around to having another round.

I am thinking IR band remote sensing, which is what JWST is doing, but has other priorities.