Surprised at the amount of people who want to change the few things that make this keyboard unique.
+1
Having endorsed this sentiment, I've been guilty of changing some things in the HHKB Pro 2 -- namely, adding silencing rings and lube. However, silencing is already an option and lube isn't in the same category as making a fundamental change in the structure of the keyboard.
I've experimented with other changes, such as swapping out 45g domes for 55g, but since then I've gone back to the stock 45g domes. In the past, I've also wished for a steel plate, but I think that a steel plate in the 60% form factor would be too stiff. I like the resilience of the plastic case-mounted switches in the HHKB Pro 2.
I can understand why some folks would like to have rubber-tipped feet, but these would not be too difficult to add to the existing model. Many 60% keyboards do not have flip-out feet; in such cases, it is easy to add self-adhesive feet or bumpers. I like a fairly steep typing angle, and to achieve this on some of my boards I use cone-shaped rubber feet to get the necessary height without requiring a large diameter. I use an extra-large mouse pad that is big enough for a keyboard and mouse, and this keeps any keyboard from sliding on the desk.
Weight is sometimes equated with build quality, but this is not a necessary correlation. I was initially put off by the lightness of the HHKB Pro 2, but then I realized that I don't pick up the board that often to notice its weight. And sometimes, I like to carry the board with me in my backpack -- in those situations, I am glad I'm carrying a HHKB Pro 2 and not a Kishsaver.
Nevertheless, if PFU or another company were to decide to introduce a HHKB Pro III, more power to them. I just hope that if this were to happen that they would continue to produce the HHKB Pro 2 as well.