We want the REPL to just work so it needs to load the module all the time as there is no extension it can look for. We don't want people to have to specify the mono module, it should just work.

One thing you did make me realize (thanks) however is that the module should only register an engine IF one was not already registered. 

I've added an conditional check for this and the new Roslyn Module that will only register IF no other engine has already been provided. This way the F# module etc will still work and not be overridden.

Make sense?