I think it's best what they are doing. Wouldn't want two teams to be dedicated to making Horizon games. They'd probably get stale that way.maybe, but I kind of doubt it. and is double even enough?
A new IP would be excellent. To be honest, I don't think it's very meaningful to look back at the Killzone sales.
Naughty Dog exploded from Uncharted 1 to 4. The first game sold a fraction of what the 4th one did. And it took years to get there. In the end it became a billion dollar franchise, but at the start it wasn't much bigger than Killzone.
SIE as a whole has blown up in the past 6 years or so.
I bet if a good Killzone game came out today, it'd sell double what Shadow Fall did.
my main problem with keeping killzone is unless they do something really crazy they are kind of beholden to the franchises establishment and those are firmly last gen.
horizon did so well in part because it went open world. let GG do another fps but when they do make it something new (for them) like a fallout or a boarderlands. it would be much better received and the kz universe isn't going to work there.
