It would be nice for mIRC to replace the IRC plugin that trillian uses... The current plugin is just not very good. I used mIRC for a long time and wrote my own scripts and whatnot but I havn't been using mIRC for about 3 years now because I just like how all the networks are in trillian but the IRC plugin is so lacking there I just don't really chat in my rooms anymore on there.
I use Trillian for all IM stuff, but IRC is definitely better with mIRC and I highly doubt you'll see any integration between the two. Best to just use one for IM and one for IRC.