That's actually where I'd like the idea to go — partner with a printing company like Moo.com and allow for invite creation and printing all from one application. Got to start somewhere, though.
I didn't put in all my ideas (since I didn't want to do "this idea, and THIS idea, and THIS idea!") but I think a threadless-like crowdsourcing on invitations would be fantastic, and a great tie-in to a Moo.com like printing ability.
I was surprised how many people use kits — I used to be part of a wedding blog where people loved to build their invites and then show everyone else for critiques. And I would cringe everytime I saw someone using italic Times New Roman because they didn't have access to nicer fonts.