This is a diagram of the Cubs state of team rebuilding. The Cubs hope that the right side of the diamond will be solid and stable. The left side of the infield will be in transition soon, as the team likes Russell at shortstop more than Castro and Bryant really wants to play third in the majors (even though he may wind up in left field). Alcantara is holding the CF spot until Almora arrives in several years. Even so, there are two starting unknowns when the team is ready to compete: catcher and left field/third.
Bruce Levine believes that the Cubs will show marked improvement next season. Peter Gammons believes the Cubs should be competitive in 2017. They may be optimistic.
The risk-reward is that the push of prospects to the majors will work out. That means the team has a cheap roster of good players under their control for six seasons. If they don't work out, then the Cubs are back to square one.
There is a huge unknown going forward: pitching. Arrieta, Hendricks, Wada may look good this year, but that is no guarantee that they will not slide like T. Wood has this season. Edwin Jackson is not an option for 2016 but he is under contract and virtually untradeable. Perhaps a trade of Castro for major league ready pitching will help.
Fans and pundits believe that even if the chips don't fall exactly to plan, the Cubs could just go out and "buy" the necessary pieces (starting pitching, closer, hitters). But the evidence points to the Cubs continuing to run a small market budget until 2020 television consolidation.
What is lost on most is the fact that the Cubs will not have the WGN TV money next year. That is going to be a big revenue hole to fill. Declining attendance and increased no-shows do not help either. If the Cubs are constricted financially by debt service and lost operations revenue, the team will not be a player in the free agent market this winter.