Our experience has been that the two things you're asking for---a shallow learning curve for learning to use a game's UI and a UI customized for each game---are

Our experience has been that the two things you're asking for---a shallow learning curve for learning to use a game's UI and a UI customized for each game---aren't compatible in practice. We arguably have the latter, a UI customized for each game, right now and it generates no end of confusion because users expect the UI not to change completely between game X and game Y. If you give the module designer broad freedom to alter the UI, then what you get are differences in game UI between games which are down to the designers being different people more than differences between the games themselves.