Though I truly enjoyed KOTCS and thought it was actually far superior to LC, I don't know how good a 5th IJ film would be - there are a lot of ways to mess this up, though if it's done right I agree it has the potential to be great.
However, if they do make a fifth one, I definitely have 0 interest in seeing SC again. Though I've liked him in other films (notably the 1960's/early '70's JB movies), I thought he was sorely mis-cast in LC, and felt that Lflm. should have gotten another, lesser-known actor. In fact, I remember reading somewhere that one of the people involved in the making of LC actually said that SC would "unbalance" the film. Plus, since Henry Sr. had passed away by the late '50's (prior to KOTCS), if he were to make an appearance he would need to appear in flash-backs - that is, unless the film was chronologically set prior to KOTCS.
That all being said, I hope a 5th IJ film is made, if only because I want to see more IJ action figures/vehicles - it seems like the only way for Hasbro (or whoever makes these) can justify producing more IJ toys would be another film. I was a big fan of the 2008 IJ Hasbro toyline, and was very dissapointed that it got cancelled before many of the planned characters were produced (i.e., German Mechanic, Satipo, etc.). And, I would like to see a re-release of the very hard-to-find TOD figures.
Hopefully this will come out in the next couple years - I don't think I can wait 19 years again