Here, I'll date myself.
In the late 50's there were darn few motorcycles even here in Northern California, one of the Mecca's for bikers. I lived near the Hells Angels Oakland headquarters,
At the time I owned a somewhat customized 1953 Harley (lavender paint, chrome springer front end), and everyone waved at everyone, Hells Angels included. When a I switched to a Bonneville in the 60's everyone still waved at everyone. Just seeing another biker was not real common way back then, so waving seemed a significant brotherhood gesture regardless of what brand bike you rode or who you were affiliated with.
Moving into the 80's and the 90's, on many different bikes, most of the Harley riders of all types tended to stop waving for the most part, for whatever reasons.
Later in the 90's till even now, in this part of the country, whether I'm on my newer Bonneville or a UJM, the Harley riders now, for the most part, tend to wave. They are also by far the most active in events like Christmas Toy Runs and Poker Runs and their overall camaraderie is quite good. Who don't seem to wave, or show up at many events nearly as much, are the sport bikes of most any brand, and usually the smaller displacement bikes.
Also, today, compared to 30 - 40 years ago, there are LOTS more motorcycles and there are times it seems like waving might be over doing it, especially on weekends on the more popular back roads where there can be a fairly constant stream of bikes (sometimes, about as many bikes as cars -- which don't wave at each other).
Today, when riding in more remote areas with fewer bikes it seems like most of the bikers wave, just like way back when there were fewer bikes on the road. And interestingly, the same kind of waving pattern happens on a bicycle around here.
Will bike waving continue ? Probably at least for a while among the more dedicated bikers until bikes become even more ubiquitous.
.