The Ledger Wallet already supports altcoins as long as they support BIP39 and BIP 32 (see https://ledgerhq.github.io/btchip-doc/bitcoin-technical.html). No changes to the chip or the firmware are required.
However, a client application (the software wallet) is needed to communicate with the chip. There are basically two solutions:
We plan to add ourselves support of Litecoin and Dogecoin to the Ledger Chrome app. Other altcoins are not currently being integrated.