The system is already in place, but without consuming plots in the cities which is fun in theory and horrible in practice (imagine all the abandoned shops, the time wasted walking from a shop to another just to search for an item; market is already hyper fragmented rn with one shop per city, imagine multiple ones... ).
What I appreciate in this suggestion is the "sandbox" part of "start a business doing such as a 'class'." . Which btw is already present in multiple MMOs, the simplest example that comes to mind is Albion Online with the refinement bonuses.