Probably best to contact Sonos and ask that, I doubt any of the users here know.

Did the Zones announcement here say anything, I don't recall. 

It did. From the announcement:

Unsupported within a zone

The following are not supported within a zone:

• You can’t add a Sonos Amp or any Sub to a zone - unconfigured or otherwise.

That ‘feature’ is ported over, as I understand it, from the Sonos Pro system, designed mostly for corporate/restaurant installations, which mostly wouldn’t use a sub woofer of any type. I don’t think much effort was made to add anything when the feature came over. And given that room grouping survives everything but power outages, I’m not sure there’s a lot of effort needed, but that’s a personal perspective. 

It certainly would be more ‘convenient’ if the zone feature included other things, but I don’t know how much additional effort would be involved. So far, Sonos hasn’t included it, I suspect their programmers are busy elsewhere, but there’s nothing wrong with requesting it, so it goes on some Product Manager’s list for future effort. 

“Zone” is intended to be used in large spaces perhaps a gymnasium or multi-room restaurant. Setup, management and operation is relatively simple. In this context a single subwoofer could not handle the situation. When a subwoofer is added to a speaker system a crossover is usually used to route bass away from the smaller speakers and send it to the subwoofer. A single subwoofer in a large space would not be very effective. In this case should all of the smaller speakers be in the crossover or only one speaker? Where should the subwoofer be located? In any case bass would tend be local near the subwoofer. In multiple spaces should there be multiple subwoofers? 

Potentially all of this is manageable, probably by an experienced pro. Even then the goal of Zones is easy management (probably operated by minimally trained people) of large systems where a few simple settings can manage a large, multi-area space. In the pro systems the operator could be remote.

In my opinion, while “simple” can be attractive it’s not always “best” for the application. For example, using SONOS for a few home theater rooms might be an attractive approach, but it should not be used to manage audio for a large multi-TV bar.