Having spent a while now working on a project with a RESTish API, I can say that I'm really regretting not pushing harder for hypermedia controls earlier. It would have made pushing upgrades out a lot simpler.
Easier for you, that is. The problem with HATEOAS is that it requires commitment on both parties (server and client) to that convention. For the client developer that means no hard coding changing URLs. But they will, and you'll be to blame when your server changes break their code. You'll say "but you didn't HATEOAS" and they'll say "my app is broken, fix your API now" and you... who wants to go there?
In this case we're in control of the server and the client, so it's less of an issue, but in general it's not the ability to change URLs that I'm getting at here, and that's not a flexibility we've needed. It's the ability to add extra functionality by adding links on each resource without breaking existing clients that I'm missing at the moment.
