You said:

I've never met a light aircraft instrument system that had a primary airspeed indicator with anything *other* than IAS, and just one redline value.

My Sailplane is licensed in the Standard category. The required airspeed markings show Vne at a variety of altitudes. In this sailplane Vne reduces quite a bit at FL180 and at FL250. As you stated the Vne numbers are IAS values.