Revamped coaching and training: hire specific coaches (the first of the various types of additional staff that you’ll be able to recruit) and assign them to boxers to grant gradual attribute improvements over time.
Rival gyms: see rankings of rival CPU gyms; where do you rank compared to your competitors? Will help to flesh out the game world.
Addition of more types of gym staff: I’m not sure yet which will get introduced first, but on the shortlist are nutritionists, talent scouts, PR gurus, event promoters…
Plotlines: Boxers will have ongoing feuds with their peers, journalists will write positive or disparaging articles about your recruits, and boxers will hurl insults at their forthcoming opponents to intimidate them during press conferences before fights. It’s all about adding more flavour to the game world.