Let me answer some of those questions so Pam or John won't have to bother.
Being multiple element, an achromatic diopter would be thick. +3.5 diopter is about 2" thick. The distance between the port vertex of a dome port and the lens element of the camera would be too far apart, causing vignetting unless of course they make a port hole big enough, which would mean a bigger housing. In otherwise, not worth the hassle to make it a flip feature, especially with a specific SWA lens.
Where do you get the 2" from Drew? The Century is 21mm thick including the threads (18mm without the threads and the glass itself even less). Granted it's a 72mm thread and the EX1 is a 77mm thread (I think) but a little zoom should get past any vignetting shouldn't it? Mark even managed to fit 2 of these stacked inside the Z1 Gates housing. As for the SWA lens, well I would quite happily remove the whole flip diopter arrangement if using that. I would only want to use it with a flat port.
A flip diopter would really be a useful feature. Typical scenario... you're all set up for macro with your diopter screwed to the camera to shoot nudis etc and then a mimic octopus swings past. You zoom right out but the shot just isn't what it could be if you could get that diopter out. Exactly this happened to me in the Lembeh Strait. The video is OK but it would be even better if I could have flipped the diopter out of the way.
However I would rather sacrifice the ability to flip for the sharper image of an achromatic. I don't think I will ever use or purchase a single element diopter with a flat port again, having used an achromatic.
Peaking and zebra seem to be part of an internal display that doesn't come out of the video out (either HDMI or component). Unless that changes in the Sony design, I doubt those features will ever be available on external monitors.
OK but allowing it to be displayed in the viewfinder would be better than nothing for a quick check. Would be a huge help with macro work.