I seem to recall seeing the .mrc suggestion before. If I remember correctly, the main issue was that if there were multiple copies of mIRC on the computer, how would Windows know which one should handle .mrc files? This problem doesn't come into effect with winamp/WMP because they only allow one copy to be installed at a time, or only one copy can be associated with each filetype.
I think it would be neat if mIRC was changed so that only a single copy could be installed, but so that single install could run as many different sessions as you want without having one session corrupt another session's files/settings. What comes to mind is to have a root mIRC directory with subdirectories that would contain completely separate data/scripts/etc for each session. When mIRC started, there would be several options to choose which session should be used (command line switches, default session, session choice dialog, etc). This would also allow the .mrc extension to be added to Windows. When someone right-/double-clicks a .mrc file, a dialog would open asking which session (directory) the file should be associated with. (BTW, I made this idea up on the fly, so there are likely to be some changes necessary).
-genius_at_work
