The scenario: A 20+-year-old legacy desktop system is being uplifted to a SaaS/web platform. Each screen contains a large amount of input fields. Traditionally, users have built "muscle memory" moving between fields using arrow keys, or the Enter key.
The question: Users have indicated that they can live with using the Tab key to move to the next field, but they are frequently moving in multiple directions in the current state (up, down, left, right) and having to constantly shift between mouse and keyboard is a major pain point identified in the research. Some users are doing almost everything with a numeric keypad. Would there be any issues with allowing users to traverse screens using arrow keys (apart from selector menus needing them)? Or should we design the new system in a way that minimizes multidirectional movement and train the users to use tab/ shift-tab to go backward/forward?