(spoilers)
I kinda figured it was only a matter of time before Cadance and Shining Armor decided to have a child. After all, they've been happily married since the end of Season 2. I have a feeling that this little side event will progress much like how the Equestria Games did through Seasons 3 and 4. Specifically, this episode marks the announcement, there will be the occasional mention at moments over some of the future episodes, with the big arrival coming probably sometime near the end of Season 6.
Anyway, with this being a Pinkie Pie episode, it was inevitable there would be a lot of funny moments (such as finally seeing the old pinball gag for the first time in the show). But one thing that really got my attention was when Pinkie Pie remarks, "I've been really liberal with Pinkie Promises lately." That, and Pinkie's actions throughout the episode, demonstrates a real hazard about making lots of promises: If you make too many promises, some of them could end up conflicting with each other, and trying to keep all those promises may lead to a really big mess.
Also, we saw that the Cutie Mark Crusaders have their cutie marks from last week's episode, so that makes this one another example of immediate mid-season continuity.
(end spoilers)