The game's sole expansion will appear on the 3DS version, should the game come out.
http://www.nintendoworldreport.com/news/28897
The Binding of Isaac will include its first and only expansion, "The Wrath of the Lamb," in the planned 3DS version, Edmund McMillen mentioned in an e-mail exchange with Joystiq.
When asked about the 3DS version of the game, McMillen stated that it is being planned. "The only news I have on the 3DS is that it seems possible but it's still going through higher ups to make sure there won't be an issue with the 'religious' aspect," he said.
If the 3DS version isn't approved, McMillen remains optimistic about its appearance on other platforms. "If we don't land the 3DS, the publisher I'm talking to has expressed interest in other digital platforms and is currently contacting them as well about the port." Previous, McMillen stated that it would not be ported to other platforms.
Should the 3DS version be approved, it will include "The Wrath of the Lamb," which promises to have 50% more content over that of the original version.