I think the potential for Jake came and went with RE6. I don't think co-op was necessarily an issue with the story, my problem was the cast of characters and how they were utilized. Helena, Piers, and Jake all have no reason to exist, but if they were to tell a meaningful story about a new character, they could have done so with Jake.
I can't stress it enough, but Resident Evil 6 would have been a much stronger game with only 2 campaigns, with a secret Ada campaign pushing it but still being acceptable as an unlockable reward. Leon and Sherry and Chris and Jake would have been much more meaningful pairings. Two veterans looking after the offsprings of their former enemies.
Not only would we finally catch up on what's been going on with Sherry, but they could have filled some gaps by exploring Leon and Sherry's relationship through the years, with Leon even taking on more of a protective fatherly role.
Chris and Jake on the other hand would be interesting purely because of the 2 differing personalities and strictly business relationship. They would be 2 guys forced to rely on eachother for survival and the greater good, with tensions boiling until the cap explodes with the big Wesker reveal. But ultimately, you want to see them make amends like grown adults, for Jake's sake, as he remained unlikable with his bratty manchild behavior just to force a half assed rivalry.
There's so much more long term development and overall better storytelling potential this way. And the campaign crossover moments could have been so much better with these 4 characters than the mess we ended up getting. Not to mention, being able to play as both Leon and Chris against the Ustanak would have been amazing. We don't need pointless subplots like Chris having amnesia and Helena wanting revenge convoluting the story.