|I couldn't tell you whether it would be worth the effort.
Off the top of my head, retrofitting a VTC onto the exhaust positions would require:
1) a rethink of driving the CAS
2) Intake cams could be used on all positions
3) dedicated oil pressure supply to front cam bearing
4) welding tabs onto rear of heads to mount VTC solenoids
5) machining valve covers to clear the solenoids
6) ECU to control it all :)
I personally view the variable intake as an 80/20 or 90/10 scenario which gives the biggest bang for the buck. If you want to reach for the last little bit of variable cam timing power potential, it will cost substantially to make it possible to test, and with no guarantee it will be worth it.