Chip Kelly is still one of the most innovative minds in football. He's had success everywhere he's been, including in the NFL. In his first year with the Eagles, he took a 4-12 team and went 10-6 and came in first in the NFC East. The Eagles were also 10-6 the following year.
I don't give much weight to the disastrous season he had with the 49ers. He took over a terrible team that had been destroyed by Trent Baalke and Jim Tomsula, and his QB for half the season was Blaine Gabbert.
I think offensive coordinator is the right spot for him. He's a creative mind, but not necessarily up to all the BS you need to put up with to be a head coach. He pretty much acknowledged as much when he quit his HC job at UCLA to become OC at Ohio State.
Pete was interested in Chip when he took over the Seahawks, although nothing came of it. A lot of well-respected NFL coaches and GMs have been interested in Chip for a long time.
And at age 61, Kelly's not one of those young whippersnappers that everyone wants these days, but he's not ancient, and I think experience still counts for something. He's seen it all, and tried it all.