Will the buildings be upgraded purely by tiers or upgrade directions?
I once saw a dev answer in a question where they claimed there will be tier for boats and are debating about what should the highest tier focus on. I am suggesting a system with upgrade directions/branches, where the players can choose which feature they want the most on the structures they build, and this branching can happen at any tier, could be focused since tier 1 or only split at last tier. Furthermore, it could be that these special upgrades branches can all be achieved, but will be extremely expensive for one to exist and maintained.
For example, maybe at the last tier the players can choose if they want to upgrade their ship to carry more cargo, have a faster speed, or carry more passengers. This also creates more variety to the game and allows more chaos possibilities.

