Well, I guess it would be theoretically possible...Disneyland's Fantasmic is set up in a similar way, and the Rivers of America and the Water Pagent storage area definately connect. As to whether it would be a good idea...eh, probably not. It'd be rough for guests who wanted to see the EWP in Frontierland and then Spectro/Wishes from the Main Street area. Plus, three nighttime shows is a lot for a park. Also, unlike DL, WDW's Rivers of America area isn't engineered to handle large crowds. There would need to be some restructuring for crowd control purposes if this were to be put into place. Not necessarily a bad idea, I just don't think it would be the best thing to do.