Hmm, not sure how well this would work really...
How would it know which instance of mirc to open the file in if there is more than one instance running?
Similarly how would it know which installation (or possibly non-isntalled (file copied)) to open the file in?
If it were possible to determine the exact installation of mirc to use, should it launch mirc performing any on start/auto connect options or should there be some sort of seperation between mirc and the scripts editor?
I agree mrc should be the default filetype extention used within the script editor rather than ini, but launching/opening a mrc file with mirc seems like it would be a messy implementation at best.