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".
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.
Jim Logan wrote: Thing is...Naughty Dog has two teams.
Team A (2011 - 2014) Uncharted 1- 3, spin offs
Team B (2011 - 2014) The Last of Us/ Left Behind
Only Team (Post Amy Hennig leaving) (2015 - 2016) Uncharted 4
Team A (2016 - Present) The Last of Us Part 2
Team B (2016 - Present) Uncharted spin offs
Sucker Punch doesn't have the man power to do separate teams.
Meh, I only mentioned Naughty Dog as they were the only example of a major company going back to finish off an old IP after establishing a new one that I could think of off the top of my head. I already knew that Sucker Punch doesn't have the manpower necessary for multiple teams and they most likely wouldn't do it as they like to focus on one title at a time.
Like I previously stated that used to abandon previous IPs when they were a 3rd party company that policy might be different now and after making Ghost of Tsushima they could go back to Infamous. You never know.