If this game were to have a spin-off or more narrative sequel, I would say that the events of Shear should be the set-up for the game, not the actual setting.
3 Months After the Events on Shear”
Depending on whether or not TRS reveals the origin of the monsters would play a huge factor into the actual storyline. If they do, than the story would revolve around the reaction to them. It’d be possible to reintroduce characters as “experts”, those who canonically survive Shear (ex. Ripley in “Aliens”).
If however they don’t reveal the source, which is more likely (where did the zombie outbreak come from in L4D?) than I’d say that the monsters are aggressively beginning to attack other colonies in the local star systems. Or perhaps delving more into the Patterson Field Effect, since that is the closest lead anyone has on the monsters motives. We already know that the monsters have been elsewhere besides Shear (Torvald’s ship, for one), so it’s completely plausible.
As for gameplay, it would have to follow in the same vein of mechanics as Evolve, and include many of the mechanics introduced to the game; jetpacks, perks, classes(?), etc. The biggest issue is that the game has such a strong “hunt” theme that to successfully execute that in a single player campaign would be very difficult. How would you have the player hunt a monster with an AI team and have the experience ruined by the limitations of AI? I certainly don’t have an answer.
As for the presentation of the campaign, you’d almost have to look to Battlefield’s campaigns to get an idea of how to present a single soldier in a battle/war that they are merely just a part of. Would you switch between different characters and their squad like CoD’s stories? Would you have the ability to swap between your squad based on what class was needed in that moment? Would it be a co-op campaign? And if so, should it be co-op only if the AI problem can’t be addressed? Both answers have many pro’s and con’s.
I certainly see potential, but I think it would be a huge undertaking, one I don’t think the dev’s are willing to undertake, esp. considering their multiplayer focused background.