The pivoting drops are a nice idea, I did some drawings for some a few years back but ended up not taking it any further. As brant said, you always need to adjust each side separately and getting them perfectly square can be problematic. There is a lot of braking force through that top pivot as well which is a possible area of failure. The Whytes seem nicely designed and made to reduce this likelihood. Even then, you still have four bolts to loosen/tighten to adjust the chain tension where an ebb does it with two.
The Niner ebb's are nice conceptually, but the execution seems a little flawed. Firstly they rely on the bb shell having perfectly parallel faces, which as anyone who has faced a bb shell will tell you is often not the case. Fine in principle except most bike shops won't have tools to face a 60mm bb shell. My other main worry is that the only thing keeping the two halves together is the bolt which tightens them against the shell. If one turns a bit independently of the other over time there is not a lot to stop it. Then you have unevenly loaded bearings and rapid bb failure. Also if you compare the weight to a Phil they are not so light as they make out.
The Phil's (and similar designs like the Thorn) just work, simple and effective. Similar arrangements have been used in tandems for over 60 years without issue, I'm not sure why some people have concerns over them.