There's still a very good chance that Jackson finds the success that he searched for in Chelsea in Manchester United, he is still a very young striker and can still do very well for a team that has real focus on developing him. As for Chelsea I think they've moved on from what he can offer them, he has had his time in the club and his time for him to leave.
Chelsea bought Joao Pedro who performed well in his first matches for them in FIFA Club World Cup. There are some good signals that Pedro can help Chelsea resolving their issue at a striker position and if he maintains such performances, Chelsea will not hesitate to sell Jackson to another club. Surely they will try to sell Jackson to clubs that are not their main competitors for Premier League title.
Yeah that's true but it would boost their morale against the next season don't for that they've won a trophy and important one before winning this FIFA club world cup so you should know how motivated those players would be. They might not dominate the league but there would be lots of improvement especially as they've bought new players to add to the squad. Anyways when mentioning teams in the EPL don't include Manchester United cause they're not a serious team.
If Chelsea did not win titles, people will hope that Chelsea can win titles and when Chelsea won a title, they though title it is not enough. It's so funny to see how people thinking like this, and I see this title is a good mark for Chelsea before a next season. They have been improving and this title comes to them as a result of their solid improvement in two latest seasons. It's not pure luckiness for Chelsea to go to FIFA Club World Cup final mach and beat PSG there with a very big difference.