I've changed my philosophy on themes.
We've always supported anything the shop wants, we just used to provide defaults. Bootstrap.
Now, I'm pleased to say we are supporting both bootstrap and Zurb Foundation 3.0 out of the box. You can still keep your old theme, just you have to tweak a few of the blocks that are passed on form pages.
Note: It is possible to keep your current theme and modify it. The variable blocks delivered by Django Market use Bootstrap 2.3 HTML mark up and Zurb 3.0
You can hand code for this in your theme / CSS. Please ask, if you have questions.
Also, please check out the Local Designer Tool. It assembles the layout template, html pages, css, js and allows designers to see local versions of their site.
Steve at great coins dot com with any questions.
Many thanks to Bootswatch......