5. The post had to do with whether or not a stills camera allowed to evolve on it's own, without having to cram so much more technology into the small case, might evolve more quickly and be a better camera in the long run. It is a question, not a manifesto.
I imagine that the development teams are divided into photography and videography groups. Would putting twice as many people into photography software improve photography? Maaaaybe, but more likely they'd just finish the work package sooner.
If there are video-specific hardware compromises made, such as an strong low pass filter (mentioned above), then it's possible a stills-only camera would be a little better than a hybrid. I suspect those situations are rare, and that no, photography wouldn't evolve significantly faster if it weren't for video.
A camera without unnecessary holes in its shell for mic, speakers, video-only connectors would be better and cheaper to weatherseal. Those holes are additional video-induced compromises and weaknesses compared to what a pure stills machine would be.
Kind of picking a nit, there. Neither a rather insignificant body weakness nor the cost of a gasket have any impact on still photography performance, any more than the presence of a mirror box impacts video performance. If they created light leaks, that would be another story entirely.