I'd like the ability to list any number of alternative nicknames, after that I think mIRC should go straight to either <mnick><random2-digit> or <mnick>_<random2-digit>. The successive underscores thing only helps up to two underscores (IMO), in which case if you want that you could add <mnick>_ and <mnick>__ to your list of alternate nicks.
I don't see much need for the "/nick " option; it's still more convenient to manually change nick after connecting with an alternative/random nick than to enter a new nick and then wait to connect.
With Khaled trying to whittle down the excess options, I think this is one situation where new options can be avoided without any real inconvenience to anybody.
