Ok, so here it is:
I put all my code on a git repo: https://github.com/andreacremaschi/Syphon-virtual-screen/tree/90c64ee2983aaa99f5ecb2b1ce548e75e75bce2c
But the application won’t work without the EWProxyFramebuffer kext driver, that is included in the installer package.
Again: since the frame buffer reside in system RAM and not in GPU RAM this is not the best solution for everyday Syphon work, but can be helpful to hijack an application video output that is not Syphon-enabled.
Have fun! 🙂