Ok, in terms of genetic lines. Ideally, if you would like to maintain a Clan of Sharingan users, you would need 3-4 males that are not direct cross of 3-4 generation deep parents.
(to prevent inbred retarded genetic pools)

Firstly, I hope Itachi had a son/daughter somewhere that can actually breed.

Madara needs to have also some offspring to breed.

Plus, Tobi needs to have offspring to breed.

Then we have Sasuke, who probably isnt as motivated to "revive" his clan after his stay with Orochimaru.

Then we need Danzou to be actually a Uchiha clan missing nin's son...due to the fact that he is actually half a Uchiha, it is possible for him to have offspring that has pure Uchiha blood.

Of course all of these is hypothetical, but hey, everyone wants it to be less number of characters. While a geneticist would prefer that more genetic pool is available, considering that if these 5 people are the only surviving Uchiha bloodlines, they would make a fine breeding program for lots of small little Uchiha.

Only bad thing is no known females bloodlines!

So I just want to throw this in, Tobi is FEMALE! Plus, Itachi's offsprings are females.