yesterday evening i had some spare time, so as i wanted to lower the clackity sound of the keys, i opened up the casing (a little safe...).
it turned out that a great amount of noise came from the casing itself, which is quite intuitive, ok.
then i hard dampened the lower casing, using multiple 'balls' of grey tack (or blue tack, which is known by hi-fi modders) so that when i put back the pcb, i had to press it to 'deform the balls'.
at the end i leaved off the top casing (it does not impact very much the look, imho) and i must say the feeling now is completely different. much quieter, and the keypresses feel lighter.
a brief try (to give an idea) could be to type directly on the naked pcb, with a dampening material underneath.