Thanks all for the feedback, suggestions, and interest. We've been doing Facebook for quite a while now, and while we plan to continue adding great new features, we're definitely going to be adding other social networks to our arsenal in the future, so your feedback definitely helps.
Google+ really is interesting to us, there's no doubt. However, the only thing we can do with it right now is the +1 button. We're hoping they open up the full API soon, which they've stated is coming, but without it, it's impossible to add users to circles, login to sites, or do a lot of the other things that would be very cool. So, for now, we can't even investigate Google+ much more than a "it would be neat" since we don't know what the API will actually let us do.
I'll definitely agree that making the next Facebook on your site isn't the best idea for everyone. However, the login functionality is still one of our most popular features, though the social features are very close behind. On this site, for example, we don't use the social aspects much (though will be adding them more after the 4.0 release), whereas the login feature is integral to our experience. Getting users in to subscribe as quickly as possible is important to us as well as on many other sites.
With that said, the 4.0 release has been rejigged a little to make development of other social integration extensions easier on us by sharing some code. When we make more, they will be in addition to JFBConnect, not a part of it simply due to the additional development and support that would be required. Pricing is unknown, and sharing and integration between them all would definitely be made as seamless as possible, as we always try for ease of use with our extensions.
As to what we'd work on next, we're planning to have a 4.0 pre-release newsletter going out this week which will have a survey attached asking what our users would like to see next: Twitter, LinkedIn, Google+. From that, we'll be deciding what to focus on next, which will be started shortly after the 4.0 release.
Finally, Rich, I found the FB Tabs plugin you mentioned, and think we have most of their features covered. Basically, our Page integration will have the ability to show a specific article from your site to user's who haven't like the page and it will be shown with no other menus or other things on it, so if you don't have a link in the article, the user won't be able to navigate away. Once the user likes the page, then your normal Facebook Tab URL will be shown, which is another page of your site. 4.0 also has the ability to use different templates for your site based on whether your page is viewed in a Facebook Page or Canvas, so you should have a good amount of flexibility to change the look of your site when viewed in Facebook. I'm sure that once 4.0 is released, there will be suggestions for improvements, but this will be a very good start.
Hope this all helps with our direction, and as always, feedback welcome!