I suppose it's not surprising really, considering that there have been two Resistance games released within about 9 months, but there are no new entries in the series currently in development. That's according to Daniel Brooke, producer for SCEE Online.
“The Resistance franchise has been exciting to work on," he told the Official PlayStation Magazine, "but as for the future we have no definitive plans.”
It's a shame because Resistance 3 was very well done and, while Burning Skies recieved what can only be called mixed reviews, I'm sure the Vita entry is better than some people gave it credit for. I suppose it's a mix of Insomniac leaving the series and lacklustre sales for both of the last two releases (plus long-term "the second wasn't as good as the first" comments from fans), it must make it difficult to want to put too much time, money and effort into another entry.
Still, I'd bet my bottom dollar that there'll be a Resistance 4 on the PS4 and by then, perhaps, more people will be ready to buy and enjoy.