I have a couple features that would be excellent to have in MIRC:
1. User Whois information
To make the whois information on users (i am from a channel that has fun w/ its nicks, so you gotta whois alot to see whos who) easier to access, it woudl be great to have whois information show up in a tooltip when holding the mouse over a usre's nick. I have tried to resolve this with scripts, but the closest I have come requires a right click, and only shows the information after the user has said something into the channel etc.
2. Server Messages
I personally run MIRC in a minimalist style, with hidden nicklist, hidden menu, toolbar, tabs etc. When I fire whois's or change my nick, and want to check for nickserv alerts etc. - it would be great to have an option to display server messages within the same window as the channel text.