I see Thunder as next in line, simply since the lines get outrageous and there was a rumor about it a while back. Lots of potential for queue effects, since you have this pretense of an abandoned mine/mining town - opportunities for playing with old tools and etc. that were left behind.
Splash also seems like a natural fit for an interactive queue, due its long lines and lack of current theming in the queue. The imprecise nature of the attraction's theming makes deciding on the queue a little more difficult - is the ride Western or Southern, was everything built by humans or built by animals (critters, as they call'em in Disneyland)? I'm imagining lots of water effects though - that could be fun.
Philharmagic could work well, but most of the time I see it the line is pretty short, so I end up just running through the turnstiles and waiting in the big foyer area. That would be a difficult area to install interactive elements given the, well, lack of a queue. Something about "magically" conducting an orchestra with your hands, like the Figment instrument effect at ImageWorks, could work well though.
I, for one, hope they never touch Jungle. :lookaroun The old-timey attraction works extremely well with its old-timey queue, and its big band era music, goofy narration, and Marc Davis-style sight gags.