Imagine, if someone would start making operating system and its applications that are just kilobytes in size. RAM price crysis would resolve in a day.
I agree with you though. If Apple open sourced os9, and the community could get it to run on modern hardware, I would run it.
OS preferences seem to boil down to "have someone else made this app work on the system" which makes it very much a network effect issue.
And if you use such an OS to boot a bloated Firefox, then there is hardly any point.