If you’re looking to sell themes here then building your own framework will be your best option.
You’re looking for plugins, not theme. And “best” is relative.
Here’s one article to get you started – http://www.iblogzone.com/2012/01/the-best-wordpress-seo-plugins-for-2012-part-1-html.html
With the pricing system on TF a $60 theme would require tremendous amount of features, not to mention absolutely unique & interactive design which translate to hours of development. The risk, work and possible return value are just not proportional enough that it entice authors to aim for this price tag.
If you feel that you have a lot of money to spend and want something less generic then just hire a professional to do it for you. Even at $60, that’s just asking too much from a theme.
Hi,
I’m currently using BBPress plugin for my support site. It’s fairly new so there’s hardly that many threads for now so I can’t comment much on my experience. So far it has been great. It was relatively easy to setup as well, and I like the idea of using something that most customers would already be familiar with if they used the forums on WordPress.org before.
The support forum is partly public so that Google can index some of the content – more SEO friendly.
Cheers
Here’s another read if what I posted earlier did not somewhat convince you – http://stackoverflow.com/questions/9327218/access-control-allow-origin-not-allowed-by
Bottom line is, you simply can’t.
Do it the smart way, use ajax + server side scripting to fetch the json output dynamically.
You can’t do that. Read same origin policy – https://developer.mozilla.org/en-US/docs/JavaScript/Same_origin_policy_for_JavaScript
Print your json output on a local file, and fetch it via js from there
WordPress has this sort of thing for their plugins for the longest time I can remember:

It serves as a warning to the user that they should probably wait until the plugin is confirmed to be working correctly with the WP version they have on the server. This is pretty much standard, and in the word of Wickedpixel, common sense. It would be foolish to tell users to ignore this warning.
Hi guys,
I just updated the license to GPLv3 and a linkback is now required. Please refer to the updated README file for more details.
The reason that I had to do this is because apparently authors here are not too big on showing appreciations to people for their hard works, not a simple thank you, let alone a proper credit. If you noticed several WP themes on the “Popular Files” had this framework, but none of them actually credited me for anything.
I know, I told people that “a linkback would be nice”, but I assumed people would just use common sense. How hard can it be, seriously?
Please, if you want me to continue investing my time & energy to improve the framework and providing free support for it then you need to give me enough reasons to do so. I haven’t updated the framework for a while now, I think you can probably guess why.
Thanks 
What were you using to build your themes before? 
I’ve used Starkers to build custom websites from ground up, and it’s really good for that purpose. However it’ll be too much work to build it into a custom framework for commercial themes. Better to just start from scratch.
If the item is not working as expected, then you can contact Themeforest support and tell them exactly what is wrong with it. List down all the issues and ask for a refund.
