BCNext had people rewrite his posts in their own words so noone could id him through his way of writing. Do you really think he would tell you if he was UP ?
Not to mention that people usually aren't gonna tell you their real name even if their not "famous".
Also, UP is the organizer of the project, but not a developer. Both Satoshi and BCNext were programmers.
Maybe he was sick of always having to code it

Satoshi was a visionary. That was what he brought to the table. When he was even coding bitcoin, it was an older style and not top notch at that time.
He had a vision. That vision brought us all here right now.
It would make total sense if he wasnt doing the coding. He would want the coding to be top notch, and he could never hide that he was Satoshi if he was the one doing the coding.
Thats my take on our fantasy here.
It's possible and it could make sense.
But we may never know. UP is a very talented leader. Would you say Satoshi had this quality?