I'm curious if you can split a pair of Vector 3 pedals (and a regular set of Keo pedals) such that the stoker has one and the captain has the other. I think it would allow you to display both riders' power on the same screen (as right and left). It might make it more difficult to do rider-based analytics, however.
Our team appreciates having power and/or heart rate data on the tandem. When we're on spirited group rides, I'll often tell my current training zone to my stoker such that she can match it. For those sort of rides, it would be even easier if she could see my power data on her screen, as well as her data. There have been times when I'm soft-pedaling to not hit the brakes, while she's motoring along; similarly, there are times that I'll be surging well above threshold to hang with the group while she's blissfully unaware of the effort.
Another good excuse for independent power meters on the tandem: we'll go for rides during which one person needs to do intervals, but the other is on a rest day. Having independent feedback is critical for those sort of rides.