@Brian:

I'm not sure I understand how the amended license terms change anything. If you release a work under a given license, you can't impose further restrictions than the terms of the license itself. In the case of your license, see clause 8b:

This License constitutes the entire agreement between the parties with respect to the Work licensed here.

Now, certainly, that doesn't preclude you from offering additional permissions - but you can't impose further restrictions.

Unfortunately, that's still what you're trying to do, with your footer links/script requirements.

Even using a CC attribution-only license, you can't stop someone using your theme from modifying it - at least, not by anything in the license itself, anyway.

I'm not trying to torpedo your business plan, or anything. To the contrary, a cursory glance through your library of themes would seem to indicate that you put out quality work (although, as a matter of choice, I don't like image-heavy themes - they still look good, though), and i wish you every success.

Rather, my point is that, by releasing the theme under a CC license, you're taking away any legal right to enforce what you want to enforce. You just can't get around clause 8b above. (And I'm pretty sure that clause is in all CC licenses.)

Of course, even if you released the themes only under your own Terms Of Service, you would still be in an untenable situation. Since the footer is part of a PHP file, and that PHP file is by all rights, clearly a derivative work of WordPress, that PHP file inherits the WordPress GPL. And the GPL also imposes no use restrictions on GPL'd works.

Now, I'm of the opinion that anything in a theme that isn't a derivative of WordPress (e.g. image files, CSS, layout/design) doesn't inherit the WordPress GPL, and so can be licensed however the developer chooses, it appears that I am in the minority in such opinion. Most in the community are of the opinion that the theme as a whole inherits the WordPress GPL.

(Sure, a lot of the "big players" in the premium theme community release non-GPL themes; they're swimming in the same murky waters, and would have equal legal difficulty trying to enforce their non-GPL restrictions.)