In that situation, you could hold them accountable and not vote for the same person come next election. But how about accessibility to your local member? Many people have a really hard time accessing their member as it is. When you grow a riding to that size, I can't fathom how members would be able to get to all their constituents.
Also, how do you decide which member goes where? Maybe you could spread them out so that it would work, but who decides that? Wouldn't everybody just run to the city centre and set up shop all in the same place? How would we avoid that happening?