Theoretically yes, but in my experience dedicated device forums tend to do better and people prefer them. It's also better for search engine ranking purposes to have individual forums with domain names that reflect specific products. At this point since all of our posts and topics (thousands of them) are all indexed on Nexus7Forum.com it wouldn't be smart to change it to another domain and many buyers really like having a dedicated forum for one device because it let's them avoid news and information on other devices they don't have and aren't interested in.
Overall, a dedicated device form works better for most in my experience. People tend to not want to hunt for news and info about one of several different devices in a forum. They like having one place that's all about their device. Hence I think three forums...one for the N7, one for the N10 and one for the N4 is the way to go. For those that have more than one...they can join each forum for each device they have. They can also discuss general stuff in 'The Lounge' but it's better to keep all the technical stuff and help/discussion topics about other devices on their dedicated forums.