The Z15 does require having a WKM as it accesses the FC IMU but that does not mean that you have to use the WKM as a FC i.e. you could still use your Hoverfly board. If that is what turns you on.
If you want to build the best then take a Z15 and put it on the front of a TDI helicopter and use the helis conventional flybarless controller plus data logger. Not a lot difference in cost to a S800. I doubt that you will have to wait that long before a Zen. 5D version comes out. I would like to see what can be done with a sony 730 and the zoom button. Auto object tracking cant be far away.....
260 KPH and rock steady in any wind. At least twice the endurance of a S800. TOTALY reliable.
So is it the seemingly easy way to get into hovering with a commercially available MR, or the fun you will have creating your own MR and against all odds and seeing it fly. Some food for though for your next comp. I won't have the time to enter.
Perhaps the question should have been WHY NOT. I could get interested in that as a subject.