@Easter Eggs
Generally I think the new gags are a product of trying not to let the old gags turn into running gags. As in, have them outstay their welcome.
In season one and two, Derpy had quite a bit of build up in presence. In they kept using her, then the gags that come with her would become stale.
Conversely, the new gags allow some to throw out some stimulation to the content starved masses after how short season 3 was.
I imagine at some point, they'll get tired of external gags at some point… And then they'll return to having a few "Light" sprinklings of mythology gags. Derpy will probably do something somewhere and then we'll all breath a sigh of relief… And laugh.
… Then they'll build up the mythology gags again as the referential gags fall to the way side, until it reaches another peak and they return to another slight shift in style to new sources for references.
It's one big cycle… Who's actions will continue for as long as it can while the creators manage to stay on top of what the audience can handle without feeling like its become stale.
And then… Maybe the reference gag of yesterday will become the mythology gag of some fart off season?
I don't know, have a Derpy.
Which reminds me… I'd like to see Derpy be depicted more often as somewhere between clumsy cute nerd and manic pixie girl…
…Hmm…
Like Mako Mankanshouku from Kill la Kill maybe? Except maybe with glasses?
(Okay, seriously, do I just have a thing for glasses? Or do I just really want to see Derpy wearing them? Or both? I don't know.)