Interesting point. However, I believe frequency trading relies on connections with extremely low latency, while satellite links are characterized by high Round Trip Time.
Geostationary satellites have high latency because they're so far up (36000 km). But dense low earth orbit satellite constellations can give lower latency than fibre over longer distances if you relay from satellite to satellite, because the speed of light in a vacuum is 1.5 times faster than in glass.
But even NYC to Chicago you have to bounce off several RF base stations due to the curvature of the earth, and each station will add latency. One LEO satellite can probably get LOS to both NYC and Chicago at the same time.
Couldn't you build analog relay stations that add 0 latency if they are for a dedicated (non-switched) connection? Where the receiving antenna pipes the RF through an analog amp and sends it out the transmit side (possibly using filtering to clean up the raw signal)?