As said in previous posts, shuttle demand definitely has experienced a passenger flow change.
But, even though I respect that you guys are concentrating on US Shuttles mainly, I'll remind you that there are many airlines all around the world operating shuttles between certain cities. And in some of those cases, shuttle operations are actually recovering and gaining more demand.
I'll give the case of my country. Avianca operates a shuttle between Medellín and BOG
of 15xdaily frequencies with a mix of MD
-83 and 757s, they keep adding more capacity, and frequencies may be elevated to 17xdaily by June this year. The thing is, you guys in the US have lots more options (like Amtrak, fast highways, etc) to take instead of the air shuttle. But to us, the absolutely best option is flying.
So, within the US, I guess that demand for Shuttles has decreased, but this may not be the case in several countries outside, although considering the general impact that aviation has suffered.