I think there's a lot of confusion going on here as to what a secondary controller is and isn't.
Yes, there are very simple secondary controllers, but they're often limited in functionality and can only control certain types of devices, lack any kind of feedback etc.
Using a gateway as a secondary controller is very different from a remote/key fob/scene controller, as most were designed to be primary controllers and nothing else.
Yes, I'm well aware Vera can do this, but SmartThings can not.
Also keep in mind that this is a Z-Wave only thing, ZigBee does not support this kind of configuration, but ZigBee does support key fobs and remotes just fine without it.
For us to make the Almond+ work well as a secondary controller in accordance to the wishes expressed by everyone in the forum and on Kickstarter would take us a significant amount of time and use up a lot of resources that we currently don't have. Sure, we can throw together something that sort of works, but I presume that's not what you guys are after?
We're not unwilling to work on this, but right now we simply can't put everything else aside just to make a dozen or so people happy, especially considering we have so many other things that we're being asked to implement, ranging from simple sensor support to fixing some fairly major issues.