Not drawing many YET. Your app needs to be somewhat far along in development in order to need real world testing. Even Marco Arment, who makes a podcast app, has said his app is not ready yet.
It’s a whole new OS in a new product category. You’re assuming what apps will be popular in visionOS, but since Apple is trying to make this a desktop computing platform, readers and podcast apps will be part of that platform.
The podcast app isn’t the point when the issue is why developers aren’t signing up for early spots now and instead pushing appointments to later.
I agree with you that "time in the oven" is wise and needed. I think putting a bit more effort into making it easier to develop would help. At the moment, it sounds like those development kits have their own challenges to entry for most devs. I also think the rate of purchase or adoption will definitely take some time.
It takes some time to become familiar with new APIs etc. But with a new product category such as AR/VR/spatial computing with so many new paradigms I would think that getting real hands on experience early is vital.
Otherwise developers end up wasting a lot of time creating concepts that ultimately don't work well in real world use. The visionOS simulator is no substitute for actually wearing a headset.
The fact that developers aren't grabbing every chance to get hands on with the hardware doesn't sound great to me. I suppose the main question is is that because Apple are not handling developer access well enough (I've seen a lot of complaints about the limited locations of the labs), or is it because developers are not interested in the platform.