Hi Bastian - are you an Extreme employee? I'm wondering where you're getting your information from - ie do you actually know what features Extreme are planning for future firmware releases?
Unfortunately we have never experienced a case where we can actually use HAU to get to a firmware version that we need. It's not a very useful feature unless you can reach every firmware version with it, as when you experience a bug that requires a firmware update, you still usually have no choice but to take down the whole system causing an outage.
VSB still gives you a single software system, so the whole thing can theoretically crash at once, and it still represents a single point of failure.
