Looking around, I notice that most of the commonly available electronic viewfinders that people might use with things like DSLRs and FS700s are of fairly low resolution - often something like 800x480. In a world where we practically give away smartphones which have similarly-sized displays significantly exceeding this resolution, this seems a bit unfortunate.
Other than the Astro's doubtless rather expensive and in any case difficult to find DF-3511 viewfinder (is it even out yet? is it still a thing?) I'm not aware of what's available.
I know there's a rather nice 720p viewfinder on Alexa, although I also know that if I have to ask I can't afford it.