With printers being a home appliance for several decades now, hasn't that always been an option for DDi?
		
		
	 
True. But not everyone can afford the costs of that much printer ink. I know I can't.
	
	
		
		
			So maybe you are right, but the burden of printing will be left to those who want it in print, to reduce costs to WotC.
		
		
	 
It's an intersting idea with a lot of possibilities if the functionality can be incorporated into DDi. The software design would be complex and WotC has always had trouble with software design.
Still,
DM's could print their own DDi-based monster books. Or a "Dungeon" adventure book. Or print out a Scales of War adventure path book.
Players could print out DDi-based class or races books. Their own Power books.
And once the software has been improved on, DDi members could share their "designed" books with other DDi members as suggestions for POD options. DDi members could band together to build the perfect player or DM resource and suggest their creations to WotC to become "official" D&D books that are sold to brick and mortar stores.
The sky would be the limit.
The process would be daunting and have a lot of growing pains, however. Yet, I think D&D fans would love the idea. Plus, it would offer the best of both online content and print products.
Imagine being able to print your own Monster Vault boxed set. Or a compiled book of Forgotten Realms, Eberron, or Dark Sun articles into one POD book.
You could choose softcover or hardcover format, or even digest format. You could choose black & white or color. You could customize the art you want in the book from WotC's online art gallery.
You could choose font type and print you're POD books in a style that matches the classic look and feel of old school products from the BECMI or 1e/2e era.
How cool would that be?