The initial idea (2004-2005) was to build a Mac tablet computer based on touch screens.

There was lots of speculation about this starting in 2002 when “Inkwell” handwriting recognition showed up in Mac OS X Jagwire:

https://en.wikipedia.org/wiki/Inkwell_(Macintosh)

https://www.macworld.com/article/155597/wacom.html

https://www.oreilly.com/library/view/mac-os-x/0596004605/ch0...

And related patent filings go as far back as 2000: https://patents.google.com/patent/US7564995B1/en