I like the idea of a Raspberry Pi SE site, but how many people even own one yet? It seems like this site is doomed to be stagnant unless [and until] more people can get their hands on one and start learning about it.
I think not. Even people who don't have theirs yet are very eager to learn more and experiment. Once they get the device (provided they preordered it), this will only increase.
As of this moment there are 5783 Raspberry Pies (how the heck do you pluralize Raspberry Pi?) put on this map, and there surely are more than these that have been received by customers. The main question is the promoting part, if that succeeds, I think we will have a lot of users in no time.
I am one of those that haven't gotten my Pi yet, but I expect it to arrive in a few weeks. Still, there might be good questions (and possibly answers) from me. If the users (or potential users) are motivated, they will still ask and answer questions.
This is part of the point of the beta phase, and while this may create issues for the site at first the flow of questions will help to determine the appropriate time to leave beta.
The initial orders of devices should be arriving within the next month or two. Until then, many people can still ask software questions.
At this stage, most people I know who really wanted one have (at least) one, myself included. If this beta went live a few months ago I may have agreed but at this point in time they're starting to become much more readily available.