You still can make a sole Magento Theme, Joomlart.com also will do such from february 2009 on and already released the first free template JM Purity. But you may know that.
The fact is, no one really needs a Joomla Bridge when using Magento, only the folks that want to switch from VM to Magento and will move a DB from VM to Magento or desperately need a CMS on the side of it will need a stable JFusion Bridge.
Just some suggestion, Magento Themes, good ones will go pretty good, also when no Joomla is around it.
Thanks! Be so kind and look for my other last post about how to make the product title to a link in the S5 Quickview Cart soon, when you haven't already, my membership expires this month already. Thanks again.