Hmm, depends what you mean by "practicable". From my experience firstly with the pre release of the first x64 version, that upgraded my HTPC from x86 to x64 and used the existing MySQL database...
In this case there's only one non-adaptive quality available.
There is work going to implement playback of adaptive streams here (GitHub - MediaPortal/mp-onlinevideos2 at YTadaptive) but I didn't...