Are you fine folks planning on getting keycaps in stock that are backlight friendly?? I know I speak for many when I say I'd love to buy multiple keycaps but I'd really hate my backlighting to be inconsistent, thanks!
Keycapsdirect does custom backlit keycaps I believe (http://www.keycapsdirect.com/faq.php#12), but I have no idea what the costs would be for that (you'd have to contact them)... I imagine it's relatively steep. It'd be a cool idea though, assuming the costs aren't astronomical. I was actually looking at doing something with keycapsdirect myself for a project I'm planning... if I ever get around to it.
Here's an example of a backlit cap they have for sale for reference:
http://keyshop.pimpmykeyboard.com/products/translucent-keys/oops