For what it's worth, it takes very little work (< 20 lines of code, IIRC) to stub out the require() function so that you can use Marionette without RequireJS. (Sadly, the project I was working on that required that wouldn't allow me to open-source that bit of glue code).

Of course, that doesn't address all the other incidental complexity you inevitably have to deal with when using Marionette.