Yes, they should just run the stereo.
There are a lot of radios out there still. Over time, that will diminish, but the cost to get it turned on is sunk, once done, having little impact.
A stream can then be stereo, if desired. Not a bad thing. And should the HD AM system improve, the stereo chain is done there too.
And the people who built HD Radios to decode it did the right thing. Those radios are simply better radios, delivering all quality modes to the listener, such as they are.
That’s why Ford always put that into their Premium units, which I’ve seen AMS in as late as 2002.
Honestly, that’s a simple line item on the list of things that can raise the value perception in the buyers mind, all of which contribute to reducing the added cost of the HD radio as a barrier to adoption.
That same dynamic works for the broadcaster too. They get to say “Stereo”, mention the stream, etc… That’s differentiated from the others, who don’t get to say that, and that’s always worth something.
Hope they have a grand time, in any case.
Here’s a great example of that oldies in stereo formula in action:
And besides, the oldies are fab in AMS! Talk about old school, period correct! Why not?