I guess the rumor that they were developing a new IP turn out to be true...
Edit: I know this looks bleak for Infamous fans as SP is known to abandon previous IPs to work on other games, but IGN had an interview with a Sony employee by the name of Scott Rhode. When question about the future of Infamous, Rhode said that Sony "will never retire an IP".
Article to interview with Scott Rhode.
As previously mentioned, SP did retire precious IP's, but that was before being acquired by Sony for their work on the Infamous franchise. Infamous is the reason why they got bought up in the first place, I doubt Sony will let that go. Besides SP is still relatively new to the open world sandbox genre so that might be using this new IP to stretch their creative muscle, just like when Naughty Dog went to working on the The Last of Us and then back to the Uncharted series.