Why go around the Earth when you can go straight through it?
[1] https://phys.org/news/2012-03-wireless-message-neutrinos.htm...
The original Kamiokande detector is still in the ground at the Kamioka Observatory, as far as i know. Hasn't been used for science since the '80s. That's about 300 km from either Tokyo or Osaka, so you probably still need microwaves at that end.
Now you just have to think of a trade with a signal in Chicago and an instrument in Japan. The CME has Nikkei futures, but they follow the ones in Osaka. Osaka has Dow Jones futures, which presumably follow the ones in Chicago, but the volume in Osaka is pretty small. Your best best is probably FX - both Chicago and Tokyo have dollar/yen futures with good volume.
So, who is already doing this, and how long have they been doing it?
The first message sent by gravity wave will be "SELL 400 AMZN"
One thing I am most excited about is the advent of low throughput ( ~100 bps) communication with the rise of neutrino communication. The optimizations needed to use low throughput link would be interesting to see.
Neutrinos may be hard to use but they at least known to be physically possible.