The Resistance series has been a major part of the first party line up of PlayStation 3 ever since it was introduced at launch. But developer Insomniac Games have a made move to develop on multiple platforms and in a recent Reddit IAmA Ted Price commented on the possibility of more Resistance.
The future of Resistance is unclear - I've said we wouldn't go back to making Resistance since we don't own the IP. But I've also learned to say "never say never."
With Sony owning the IP a sequel could certainly be in development elsewhere.