"Speaking in a recent Three Speech interview (Part 1, Part 2), Naughty Dog co-president Evan Wells said Uncharted was developed as the first part of a franchise, and we are likely to see sequels in the future:

"We developed Uncharted as a franchise. The pulp action/adventure genre lends itself perfectly to serialisation and continued episodes, which is one of the reasons we were attracted to it.

[Regarding the team’s next project] …but even if we don't do an Uncharted sequel right away..."