Dean Martin or Jerry Lewis (separately) would make an interesting character. I wonder if they could portray Jerry Lewis without his suing them?
George Wallace, but I don’t know how they’d do it.
Lucille Ball.
I think the headliners would be a little too obvious, since MM fans enjoy the arcaneness. Instead of Dick & Liz, better Dick’s ex Sybill, who opened a discotheque named “Arthur,” after the answer John Lennon gave to the question “what to you call that hairstyle?” The more obscure to 2010 the better.
Hunter S. Thompson, as portrayed by Johnny Depp.
Twiggy (in due time of course).
Would love to see some of the character’s reactions to the “Bewitched” episodes in which Darren & Larry Tate have to pitch a campaign to a new client, and the Mad Men’s assessment about how realistic the TV depiction of their career.
Kubrick. I have no idea why he would be there.
Phyllis Diller.
Hillarity ensues.
Thomas watson, Jr. the CEO of IBM during the 1960s. In 1964 IBM introduced its System 360 – the first non-mainframe computer system. Fortune magazine called it “the $5 billion gamble.”
I’d love to see Don and the gang try to develop a campaign for it.
Stan Freberg (or at least a fictional character who closely resembles him). If only just to contrast Sterling Cooper’s homey, staid, and humorless ads with those that took an irreverant and tongue-in-cheek approach.
And, for the same reason, Jerry Della Femina.
Not exactly what the OP was asking for, but I do have an idea for travel episode that could be intersting. SCDP is doing a campaign for Intourist and a Don, Peggy, & Pete have to actually go to the Soviet Union on a business trip. I know the Soviets did allow Westerners to visit as tourists (keeping to planned itineraries itineraries and staying in special hotels) and spend their hard currency, but how plausible would that plot be in 1964? My great aunt made a couple trips to the Eastern Bloc, but I think those were in the 70s and 80s.