First of all, thanks for suggesting a feature to improve Firefly III. I appreciate your input.
There is no formal roadmap for Firefly III. However, I try to release a new version of Firefly III every month. Check out the roadmap on GitHub to see what is being considered for future versions.
Some features are already on the roadmap, so be sure to check it out. Others will probably never make it into Firefly III for various reasons. Here is a (short) list of commonly requested items, that will probably never make it into Firefly III:
Sub-accounts, sub-categories, sub-budgets, etc., will not be featured in Firefly III. Generally speaking, these do not add meaningful information to your transactions.
The ability to share a financial administration with your partner or significant other. Unfortunately, this requires a large change in Firefly III's architecture and functionality. As an alternative, you could share the login details with each other.
Firefly III will not support stock accounts, investment tracking, real estate or other features besides basic personal finances. If you're looking for something like that, please check out GNUCash.
Firefly III won't support the ability to predict expenses, give you a look into the future or do financial planning. The present is hard enough to manage at the moment.