Several months ago, I looked at a common hardware component used by bitcoin miners and the thought occurred to me: this might be useful for creating additional seats. So I went to eBay and purchased one, tested it, and uploaded a short video:
The long story short is, it works fantastic. I have a motherboard with only two PCI-Express 16x graphics slots on it, so that's my theoretical limit for seats: 2. But because I also have a single 1x PCI-E slot I can take advantage of that and use the riser to plug in an additional third 16x card, giving me a third seat.
My thoughts are that if at all, this setup would primarily be useful for anybody who has a motherboard with only one single 16x slot on it. That would negate buying a whole new computer or even another motherboard if you are against such a thing. Just add in another 16x slot using a 1x slot. Just be warned, this setup cannot be used for high end gaming on the second slot. One single PCI-Express lane has more than enough bandwidth for day to day desktop or internet usage, but it would be bandwidth starved with a large real-time 3d workload. All gaming would have to be in connection with whatever video card is in the first slot.