It will be, if you can solve logistics/customer service.

A seller should be able to ship a box of stuff to an address, make a listing and then collect satoshis as orders roll in. On the flip side they should be able to pay someone to handle returns and other customer service issues.

If they do decide to handle everything themselves, the User experience should be the same. That way we can have competing drop-shipping services plus DIY all in one interface.