I collect the list of Magento 2 design themes here: https://mage2.pro/t/232
It is not so big yet
Is there any reason why there are no Magento 2.0 themes on Magento Connect? Bowsing themes, you can only select up to version 1.9.2.
The Marketplace (Connect) for Magento 2 design themes and extensions is under development now.
Our team is working on the first Magento 2 theme - Crafts at the moment. If you're not in urgent need, please check back within next 2 weeks. For now, we have a sneak peek on Craft's primary pages and feature overview via - https://www.ubertheme.com/magento-news/preview-crafts-premium-theme-magento-2/.
Oct 4, 2016 Update: We have a few more Magento 2 in place now.
- UB Mago (for fashion store)
- UB MegaMall (for Amazon-alike marketplace)
- UB Bookshop (for bookstore)
Hope it adds one more option to your list
Recently I found a responsive magento 2 theme for multipurpose store with powerful admin panel. Preferable template for online business people. Check this: Aliana Magento 2 theme
One more candidate for Magento 2 theme - UB MegaMall. Other two themes UB Bookshop and UB Mago are in development progress now. Hope you will soon have wider options to start your Magento 2 stores.
PS. Update 23 Aug: our UB Mago preview is in place now.
Themeforest.net, search for Porto and then click on the Magento 2.0 link under versions to list all the Magento 2 themes around 30 at the moment. Be aware, many of them are ported from Magento 1.x and they haven't been tested correctly for hosting environments, as we found out launching a site last week, had to get the senior developers involved. For reference, people have issues obtaining refunds even if the themes are not up to standard.