if webcam support is added, the mirc WILL continue being a text based client, because MOST of people will use it only for text chatting.
it's like a addon for video streaming (that actually is possible with some dlls); but, will create a standard for this, that a addon cannot create. the size added or the speed lost will be insignificant, because it's a module that will be loaded only when needed and IMHO it's a simple code.