Definitely not an area your average web-developer can just drop into. I can definitely write the code but you also need a good artistic/design mind. Just to make everything more coherent and to create a real theme that runs through the template.
I've been considering doing the same thing with some of my sites. Do you have any tips on refactoring something we've designed and selling it on a theme marketplace? Are there specific site features that sell better than others and/or are requested a lot? Do themes with wordpress/php included sell better than ones without? I'm very curious - thanks!
If you look at other themes on TF you will notice how many features they have. Building your first theme with the same amount of features would be very time consuming. I went with "Getting Real" approach and focused on doing the fundamentals right. At the time I launched there were no customisable fonts, colors or sidebars (something that most of other themes had). But it still sold well, because people liked the way it showcased their portfolios.
Do a Wordpress theme. It sells much better than HTML only and selling price is 4 times higher.
I've contemplated converting some of my custom WP themes to sell on ThemeForest but I didn't think it would be worth the time.
edit: I often wonder if it would be worth it to try to compete with theme clubs. They seem to make a killing on recurring revenue and release a couple of themes a year.
There are a couple of high-selling authors on TF that established their theme clubs. They build up customer base using TF and then invite people to subscribe for a yearly fee to get access to all of their themes plus the ones to be released. I guess after you reach certain amount of customers such model is much more profitable.
Eg. http://www.themezilla.com/ and here's a link to their TF profile http://themeforest.net/user/OrmanClark
In general people spend a lot of money on themes. I think you might be better off competing with themeforest or more likely, any of the number of bootstrap theme website popping up.
You pay yearly to access to a bunch of quality themes. They pay out 50% commissions (and on renewals too) to affiliates but they have 200k+ plus users. They have to bring in a couple million a year.
I believe they started out at much lower prices and started raising it as they released more and more themes.
Direct link to the demo: http://inthe.me/demo/fluxus/
The interesting thing is that you can't control the price of your theme and it is set at the time of publishing by TF. Price range for WP themes is $35 - $50
Pluginbag offers 80% to the seller with No Exclusive lock in
Shoppers will benefit from the latest, well managed and quality work of the sellers.
PS: I'm the cofounder at pluginbag.com
Hope it works out, sounds like it's a better deal for sellers (which often makes buyers happier in the long run).
Made a portfolio website for my girlfriend. Got positive feedback, refactored into Wordpress theme and published on ThemeForest. Not 100% passive as I spend 3-4 hours per week for answering support emails.
ThemeForest is a perfect place for passive income if you are a website developer. At first it challenges your skills as you need to create the concept, design it and code it. Then it challenges your business, marketing and support skills. You become a one man factory and learn a lot.