To be honest if I were Sony if Shadowfall doesn't prove to be successful, and by that I mean at least sale 2,500,000 without bundles then I'd cancel the series and have Guerilla work on something else.
Killzone never became the flagship exclusive Sony was hoping for, I mean none of the games have sold over 3,000,000 and they had great marketing and big ass budgets, but anyways.
Honestly I wouldn't be surprised if Mercenary was better considering another studio is working on it, a studio that used to be R&D or some shit.