From what I can tell, almost everyone who wants to work their way up the office ladder (at least in ATL) starts as a duty pilot. They get some very hands on work with many different departments and really see how the whole operation works. It's not a direct requirement to be a duty pilot before moving into the chief pilot's office, but it seems like the vast majority in ATL have touched that job before moving on to be an assist chief pilot or chief pilot. As far as special projects, a lot of that seems to be who you know, and the groups who are the most connected seem to be chief pilots and line check airman. I'm sure they pull regular line pilots in for stuff, but again they're going to want to know who you are and why you'd be a good fit for that job so connections still matter.

There isn't currently a job posting for any duty pilot positions, so I don't know what the min quals are, but I'd imagine it would still take a couple of years of experience at Delta before you'd be competitive for that job.