Thanks for your thoughtful post. At the risk of going further OT–perhaps the mods can move this conversation elsewhere?–I’ll reply. 
I think the term customer is too broad to be useful here. Whilst a customer centric approach is laudable it is imperfect without understanding who customers are and what they truly value. How do we define value when it varies across stakeholder groups? What happens when one group doesn’t completely understand the product vision?
This is why I disagree that Roon should invite the forum to participate in sprint reviews. I doubt that this would work …actually I’m fairly certain it wouldn’t work. For instance, when Roon makes it abundantly clear that no means no, not no for now the topic won’t go away. So maybe Roon does engage with their customers in other ways. That said, they do listen to the forum and we do influence outcomes.
Finally, I would say that rigidly following any methodology is flawed. It is the map not the territory and adjustment on the ground is usually needed.