My understanding is that code for Rpi2 would have to be recompiled in order to run it. We can't recompile the Titan code because it contains proprietary blobs which are used to run the FPGA on the controller. Those blobs were not released by KNC because they did not own them, thus did not have the authority to release the source code. Thus we're screwed.
The fpga code doesn't need to be recompiled, either fpga loader will load the fpga code for titan or neptune as needed.
Try taking a normal pi and running an update on it. If people really want me to do this I'll do it for the hell of it as I have a Rpi2.
Edit: Running now. Will take forever, what the hell.
C