penmenship doesn't matter here is 1 reason why:
it's worse on your hands than a mouse or keyboard.
why keyboards won't fade even with touch is simply because writing by hand, is bad for your hands and bad for your eyes as it requires far more strain on your eyes (looking at back-lit devices puts extra strain on your eyes)
math should be done in writing, only because it's faster but text is wholly unimportant and the movements for it are completely unnatural (unlike educated use of a keyboard. which due to the use of board games over several centuries have caused us to be far more naturally adept towards than writing by hand.)
and to nostalgia freaks: writing with a pen is about as new as modern as the computer (only the elite of europe used to write in the 17th trough the 18th century).
writing text is too inefficient to proceed doing it by hand, eventually keyboards will faid and our minds will be the input device until then keyboards are here to stay (especially on touchpad devices)