They most likely will,  Coinbase recently hired Charlie Lee  (Coblee) the creator of Litecoin.  He has commented that they will consider doing so, but not yet, due to the fact the cryptocurrecny is too new to the world still.  They are still getting people to understand Bitcoin, adding another coin would only confuse and frighten them, hurting the crytpo movement in general.   yes all  BTC exchanges allow for BTC transfer between them.  Same goes for LTC exchanges.  Coinbase does allow for trading of BTC in and out as well, though it is not an exchange, per se