FoMoCo have done a lot of development work on this concept. Right now the principal downside for racing is weight. It may never be possible to make it weigh less than a conventional cammed valvetrain. The obvious upside is the same freedom in valve timing as allowed by a solenoid system. Either can be controlled electronically. I think that some of the components in the illustrations could be shared by more than one cylinder, perhaps an entire bank. This would get the weight and complication within reason. Ford has made single cylinder prototypes which are very promising.