I dont know enough about multithreaded programming to offer an educated opinion either way, mostly because i have yet to find a situation where it would have greatly benefitted any of my projects.
If you really want to put your point across, the best way would be to provide a practical example (perhaps with pseudo-code) of something you could do in mirc with the addition of this feature, that would otherwise be inpractical or overly troublesome.
It would also benefit if the example is related to IRC, and not something that probably shouldnt be done through mirc in the first place, although either way go for it...
