Mad Men/WMG

The Draper kids will experience Soap Opera Rapid Aging Syndrome if the series lasts past about 1967, possibly before.

 * At their current ages, Sally will still be too young to drive when Woodstock occurs, and Bobby will still be in High School when the Vietnam War draft ends. The series has already shown a desire to hit on every turning point of The Sixties, thus older kids are needed.
 * They don't have to be involved in those events. For example, with the Vietnam example, they could have Don Draper interacting with some of the draftees and volunteers, and him feeling the differences between Korea and Vietnam.
 * Less likely to happen now that Kiernan Shipka has been elevated to regular status as of Season Four. Word of God is that she gets more to do each season because she's an actor, not because she's cute.
 * Glenn's back in Season 4, and it looks like they're pairing him with her. This could go lots of places; since he's played by Matthew Weiner's son, they can pretty much bring him back whenever they want without losing the actor to another project.
 * There's also the amount of turning points missed, such as the civil rights movement, the barely touched upon pop art during that era, the Beatles and Rolling Stones, the radical feminists, and that they wrote out Sal mere four years before Stonewall. From this point of view, it rather seems that they are going out of their way not to touch upon the turning points.
 * Events of the Civil Rights movement are seen on TV, and Paul Kinsey travels south with his African American girlfriend Sheila to take part in the marches. Nothing much about Pop Art, granted, but boss Bert Cooper owns a Rothko. Sally and Don go to a Beatles concert, and Don gets Sally a Beatles album for Christmas. The feminist movement came later. And, let's face it, the Big Events of the 60's have become predictable. It's refreshing when a show integrates them into the characters' lives but they aren't the main focus. The big exception was the Kennedy assassination.
 * Pretty much Jossed. They're talking Emmy nod now for Kiernan because of how much Don's home life turns on her. While the Beatles are getting touched by her and Don connecting and it's Don who gets the stones as his power walk music. Peggy is going to be the one dealing with sexuality and feminism though.

Don really is going to write an autobiography.

 * Maybe he was kidding when he said it to Roger in Season 1 but after the events of all these seasons maybe he decides to use his flair for words to put his life into perspective.
 * Maybe he'll follow Roger
 * In one episode, he stated that he was a "lousy student" and never wrote more than three consecutive paragraphs before in his life. On the other hand, that was when he was starting a journal, so maybe he could build from there.

Don is the guy jumping off the building in the opening credits.

 * Which could be the ultimate foreshadowing with Don at one point attempting suicide.

Sterling is the jumper in the credits.

 * After the whole fiasco, he's looking dangerously close to losing it entirely.

Grace Holloway is the daughter of Joan Holloway

 * She's just the right age and they look a bit alike, even having similar red hair.
 * Where does Grace Holloway fit into this?
 * Maybe she's distant relative who Joan decides to name her daughter after.

Lane Pryce is related to Wesley

 * Or Mr. Hooker! They share a certain ineffectuality.

Sterling is related to Roger Sterling.

 * And inherited the Deadpan Snarker gene.

Don and Peggy will hook up

 * Don is widly believed to be based on an specific advertising great who started his own firm and married a former secretary who became a copywriter.
 * This seems really close to happening as of episode seven of season 4, but is averted for now.

Trudy Campbell will have a miscarriage

 * You know to spice things up in their relationship.
 * JOSSED. Trudy and Pete are now parents of a perfectly healthy baby girl.

The early '70s were/will be lean years for SCDP.

 * The bad days will begin when cigarettes are banned from advertising on US TV in 1970 and end when the first Honda Civic debuts into the 1974 oil crisis. Since Lucky Strike is Sterling's pet account and Honda is Campbell's, this will set up a very interesting dynamic to watch.
 * The basics of this may still happen, but as of the most recent episode Lucky Strike has dumped SCDP setting the lean years up in the mid 60's.
 * Also, the Honda Civic is precisely the car account you would want to have going into the oil crisis. SCDP's execs viewing the Civic account as a mere consolation prize is a case of It Will Never Catch On, and possibly foreshadowing if indeed the show's story takes the firm into the 70s. Between quieting tobacco ahead of the rest of the industry and landing a fuel-efficient economy car account a decade before the oil crisis, SCDP is poised for a huge comeback in the 70s.

Samsonite=alcoholism for the Mad Men writers.

 * Thus far, of course, we only have the evidence of "Six Months' Leave" and "The Suitcase," but it is kind of interesting that two episodes that deal with alcoholism also involve Samsonite in some major way. "Six Months' Leave" is kicked off by Freddy Rumsen passing out and pissing himself during a pitch to Samsonite, and "The Suitcase," which showcases the beginnings of Don's inevitable alcoholism (the puking should be a clue) and the depths of Duck's (every time he shows up), as well as mentioning how Freddy is now that he's joined AA (Roger isn't pleased), gets its start with Don and Peggy working late on the Samsonite campaign.

Megan is not her real name/she is hiding something

 * "Megan" was a really rare name in North America in 1940 (when she would have been born), even less so for a French-speaking household in Quebec. Either she changed her name when she came to New York, or she's Don's counterpart in more ways in one...
 * She seems to smirk when Don's not looking implying she's been working toward her goal in being the new Mrs. Draper.
 * Word of God indicates otherwise, with Matthew Weiner and Jonathan Ingla being very clear about Megan's sincerity in the audio commentary for "Tomorrowland".

The guy falling in the opening sequence is no-one

 * It's purely symbolic of their lives falling apart, not a specific allusion to someone attempting suicide.
 * It's mentioned off-hand in one of the commentaries that one of the junior executive characters (likely Harry Crane) was going to jump off the SC building early on, but the writers decided they like the cast too much to do it, turning the credits into The Artifact.

In Season 5, the cast will go see How to Succeed In Business Without Really Trying
The movie came out in 1967; Season 4 ended in 1965, so Season 5 will start at least half a year later. There's no way they're going to miss out on a Robert Morse Casting Gag.

The company will now be Sterling Campbell Draper Pryce
With Bert gone, they don't even have to change the initials. Additionally, Ken Cosgrove and Harry Crane might be added as partners.
 * Bert seems to have changed his mind about leaving in between Seasons 4 and 5.

Pete and Trudy are Annie Edison's grandparents
Per this Jezebel comment

The silver/red interior '65 Coupe de Ville is Don's last Cadillac, for a while at least.
As he gets into his mid-40s in the late '60s he's likely to want something sportier and more youthful, and that '69 or '70 model (Mustang? Corvette? something European?) will be due for replacement right about the same time as the aforementioned 1973 oil crisis.