alt Hacker NewsProbably few. The US has excellent observers and comms sats by the dozens are not very big. It's true you can get some photos but the kind you're thinking of, where you can track vehicles in a meaningful way or something, has to be done by something closer to the hubble telescope (pointed backwards).
Even if it would just deliver 1 or even just 10 meter resolution, I would imagine the high revisit frequency would make it commercially valuable, and potentially also provide some value to military/intelligence groups because it would make it harder to hide activity through careful timing and the data would come with fewer secrecy requirements.
And I have no clue what is doable with SAR, but I'd imagine multiple satellites following each other would enable some interesting features, as it essentially gives you a giant antenna.