The multiple server connect on startup suggestion has been made before, I think more than once. One such time is
here.
I think this would be a nice feature. As you can see from above though, it's very easily scripted and as far as I know, as scripting
is an mIRC feature (I mean it has it's own scripting language) things that are easily scriptable generally aren't turned into features.
I could also see it as being a little annoying....let's say you want to only connect to one network for a quick 10 minute chat (I often do this in the mornings) - you might not want to connect to all 3 networks, because then you have to say "heya" to everyone and then "bye" to everyone, which can take up that 10 minutes without even chatting! You would have to quickly go to each network window and disconnect it quickly before you connected and, perhaps, automatically join your regular channels...it'd annoy me anyway!
My 2 cents.
Regards,