8. Bill & Ted Discover Metal
This is probably the least likely to be successful of the listed scenarios due to the nature of casting child actors, but in this version of Bill and Ted 3, our heroes must go back in time to meet their young selves, then at the age of 12, to get them into metal so that they can later become the worlds saviors. Having older Bill and Ted attempting to influence younger snottier versions of themselves could be entertaining. This would allow the franchise to return to an 80s setting, which could bring in some cameos from some of the metal gods of that decade.