I will admit right at the beginning that I haven't used whatever DLNA support Windows 8/8.1 has built in.
I've seen something to that effect in the Share charm before in Store apps, as I recall.
Whether this applies only to media like audio and video within certain apps or individual apps, or is a system-wide experience, I am not clear.
What I would like is to have functionality added where I can add virtual monitors which can be broadcast to DLNA receivers that are in range (in the traditional screen resolution menu where you can see all monitors which are attached to the PC).
In other words, mirroring my screen to nearby DLNA compatible TVs etc. is good, but if I want to extend my desktop wirelessly to a nearby TV or monitor, that ought to be possible for the most novice user and it should be organized with the rest of the controls for managing connected displays' resolutions and physical arrangement.