There is still a long way to go. I've seen plenty of attempts and the Fiat multiair is by far the closest real world application but it controls hydraulic pressure to close the valves rather than open them (although it can do that at low revs which suggests this is a pressure/flow limitation of the design). The multiair design raises a lot of questions and "why have a camshaft at all?" is the least of them. "Why only control one side?" is the starting point. Either there is nothing to be gained in modulating the other side (hence 3 lobes per cylinder on a single camshaft) or the design simply doesn't permit it. Whether this is a limitation of the oil system, hydraulic components or the engine in general is something I'd love to know mostly because it has a big impact on what can be achieved for tuning the engine. I suspect the issue is that it a matter of diminishing returns - the current design is a sweet spot with any improvements making little impact on performance or efficiency.
Mercedes have shown you don't need any of this to make an immense improvement in efficiency although it does beg the question of what could be achieved with both sides of the bargain - Fiats multiair and Mercedes' compound charging. The result should (in dreamland perhaps) be a superbly efficient and versatile engine with unbeatable efficiency for an ICE.