PSU: whats different from extra mode and online mode?

[Zeppelin36]

i know online has REAL people. but offline doesn't. but is extra mode basically the same as online mode but with no people?

[Diablohead]

There are different missions and its easier to find items and meseta offline. In the end online will have a lot more content.

[ThundR]

Question:
Does anyone think it's possible that any online missions will wind up in the marketplace to be used in extra mode. I'm having a blast offline so I really don't see myself signing up for online anytime soon. I remember at one point you could download online missions for an older version of PSO. I think for the DC but could have been the GC...can't remember.