I have almost completed being able to make a Joomla Theme work in WordPress.
The person would have to have a full Joomla Theme, then add around 8 files to those files and they would have a theme designed for Joomla, working on WordPress.
8 files seems like a lot, but some of them you basically have to have, page.php, header.php, footer.php, archive.php, functions.php, there is 5 already, so maybe 10 files total.
10 because I have eliminated the widget files, yes, the widgets still work and if you changed themes, you would not have to change a thing because the other them would have those widget files with it.
I have it set up that all original module positions are available. If the module position is not being used by a widget, it does not show up. You could start out with 20 module positions.
Now, just have to work on a few minor things to have more options available for making design changes to the widgets like in Joomla.
By uploading a Joomla theme to the theme folder, then adding these files, it would work in WordPress, so they would need the original file from the Joomla premium sites.
The bad thing is that since Joomla themes, not one is set up the same, each theme will need 8 different files to match the theme.