Tim Goodman makes the case for Don's spiritual enlightenment:
"In the wake of what will likely go down as one of the best (and better received) series finales in television history, one bit of Mad Men analysis has baffled me: the cynical take on the ending — that Don Draper didn't experience any personal enlightenment and merely came up with a way to sell soda to hippies.
Not only is that view slightly blind to the evidence presented in the actual finale, but it's also willfully dismissive of all the episodes that came before it."
http://www.hollywoodreporter.com/bastard-machine/mad-men-series-finale-tim-796826
Worth the read.
I don't read much online commentary, but there are really people who think the ending was "old" Don Draper cynically cashing in on the counterculture? That seems a singularly misguided reading of everything we were shown about the direction Don has been headed.
Watching again and thinking about it, the more I think the ending is fairly unambiguous. Don made the commercial. Peggy making it is no revelation, she is the up-and-coming generation, we know she is headed up while Don's generation is on its way out. For Don to make the ad, though, that's a breakthrough. It shows him transcending the limits of his generation, persona and past. The guy who instinctively hates the Volkswagen ad can't make that commercial. The guy who can't finish listening to the Beatles record can't make that commercial. "Don Draper," the impostor, can't make that commercial. If Don isn't the main force behind the commercial, the finale doesn't realize its full potential.
The even put the yoga gong in at just the right spot like the "ding" of an idea light bulb!
If he made the commercial for McCann, that doesn't mean he'd stay at McCann. The headhunter told Peggy that after putting in a few good years at the biggest agency she could go anywhere. If Don made a commercial as big as the Coke Hilltop at McCann, he could pretty much write his own ticket.