I saw in the latest changes that the drivers for the Vu+ 4K boxes support QuadPiP now. What surprises me is the fact that I haven't found anything in the forums here about it.
I downloaded the images of the 25th and 26th but couldn't figure out which one might include this feature. There was also mention of a plugin that might be required, but that's the only place I heard about that, too.
From Erik's remarks I deduce that there are serious issues to get it working under Openpli (soon) and that there were problems with the drivers as well (what were those btw?). So I tried VTI to check it out and it didn't work 100% (especially not with a Solo 4K) but well enough so that I would miss this feature if not included in Openpli, much more than HBBTV or other stuff.