The way you were talking about GTK, it sounds like you have somewhat of a technical background, and could follow that discussion. As far as I can tell (I don't have any technical background, and I can't follow the discussion) this is a new feature which was just added to a development version of Inkscape (or maybe it was added to a trunk, in case a trunk and a development version are not the same thing).
I guess you would need to install that....either development version or trunk. Except that I've seen some messages on the mailing list about problems with a new trunk. From what I can tell, it sounds like those problems might be related to this new feature.
So I would not jump into this right away, unless you really know what you're doing. I would wait until it's released, at least in some relatively stable development version. Moini will have to correct everything I probably said wrong. And if it is available in a dev version, she can tell you where to get it.
From what I can tell, this feature is being developed much more quickly than what we usually see. I think there is a big push underway, to finally release the long awaited Inkscape version 1.0. And I'm guessing this is part of that.
I can't really say how long it will be before it's available in a relatively stable version. But based on the speed this is happening, I would guess a week to a month -- unless they hit some snag that they can't fix, which of course is not something which can be predicted.