I'd never use one for playing a piano. It was designed with Groove agent one in mind primarily, and therefore tapping pressure feedback is fundamental to its function.
Yes they can also be used as a set of programmable function keys as you state, but they are still physically touch sensors and not buttons - there is no tactile feedback (you must have noticed), and this makes them unsatisfactory to an extent as buttons especially when you also want to eliminate the visual feedback as well.
But I know what you are trying to say, and should they consider your suggestion, you must realize that this would have to be a user option, specifically for this one controller, and not a fixed operational mode like the dim function.
To that end, you're going to need a lot more people wanting the feature you describe to have it be considered for implementation.
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