I guess for North America yes. Out here a touch lower, but people seem to figure it out. On a previous posting I had suggested trying to revive JT9 or JT65 to create “watering hole” frequencies for hams in fairly high population countries to find each other - the idea being that it would give people with one element antennas running barefoot a chance to work DX (each other). Maybe FST4 could be the mode for that? Maybe always 1 kHz below the FT8 frequency?
More FST4 activity is on 630m. The 160m FST4 is very rare, see pskreporter.com. But nothing prevents us to make it more populated. Well, physical limitations of FST4 protocol might, but we will not get deep into the theory for now.