What about the flashback portions of Ant-Man with Haley Atwell (Peggy Carter) and John Slattery (Howard Stark, which is cool they remembered him from Iron Man 2!)? Do we know anything about that yet? Also, will they ever show Maria Stark?
Other than that there will be a flashback scene to the 1960's with an older Peggy and Howard Stark, not much else is known about it. Presumably the 1960's era Peggy and Howard will contact a younger Pym about his technology. Until they release a trailer or expanded synopsis, we probably won't know the specifics of that scene until release, unless it's featured in promotional material heavily.
As for Maria Stark, who knows? MCU Tony was born on May 29, 1970. This means Maria became pregnant with Tony around late August/September, 1969. Presumably Howard and Maria were married before 1969, but who knows how long?
Maria has appeared in a flashback sequence of the Iron Man 2 - Public Identity #1-3 comic (which is official canon), as did an older Edwin Jarvis as Howard and Maria's butler, and later as Tony's after his parents died.
As for when the MCU version will be officially seen onscreen? No idea. I'm sure it'll happen eventually, likely on a future season of Agent Carter. As to which season? I'd say at least a presumably made AC season 3 or 4. Since Season 1 of AC focuses on the time before the AC One Shot, I'm hoping Season 2 will pick up a year or two later with Peggy actively building SHIELD and Hydra actively infiltrating early on, and hopefully later seasons can jump ahead a decade or so, so that by Season 4 they're in the early to late 1960's. Even have Slattery come in as Howard Stark in Season 4 (much as I'd miss Cooper, in terms of continuity it just makes more sense, especially since they're re-inforcing the Slattery as older Howard with his second appearance in the role in the upcoming Ant-Man. The final season can end with Howard telling Peggy that Maria is pregnant, alluding to Tony Stark's birth.
Of course, it's also possible that they'll just focus the timeline in the late 1940's to early 1950's entirely, which is just as likely. And the series' length depends on ratings, which admittedly should be good based on fan interest. I can easily see it getting a Season 2 announced by February, 2015, again serving as a mid-Season break replacement for AoS next year/early 2016.