I took a peek at what’s been happening in the @omgcheckplease fandom since the main pairing, Zimbits, became canon on Feb 26, 2016.
In brief: there’s been a huge surge in activity in the fandom in the less than 2 months since the canon first kiss! 45% of the Tumblr fandom tag activity in #omgcp since Summer 2014 (the earliest activity I could find) has happened since then, and 27% of all AO3 fanworks have been posted or updated! (I said in the chart above that they were published since then, but actually, previous WIPs that have updated since Zimbits got together would also have been captured in this stat). And the daily posting rates have also jumped 2.3-6x on both platforms.
It looks like I was far from the only new fan to take an interest in the fandom after hearing about the canon queer pairing – although I’m sure some of the activity is also generated by joyous fans already in the community, I’d guess that an increase of this size signals a whole lot of new fans as well. However, the methods of a fandom analyst like @fffinnagain are better suited to answering questions of how many new authors have entered the fandom!
[Edit: and in fact, Finn did so!]
The types of fanworks that AO3 creators have been focusing on more in the wake of the Feb 26 comic are mostly not so surprising. There’s a lot less focus on getting them together, or what their first kiss might be like, and more on how they’ll come out to others. And, as is no surprise now but would not have been predictable before Feb 26, Texting has seen a huge surge in popularity. :)
As for other trends, I’m less certain. Will Friendship and Future Fic both continue to decline? Will both Fluff and Angst both continue to rise? I think it’s probable that several of these recent trends are temporary phenomena, as we have very little post-Zimbits data yet. We’ll have to keep watching!
Going back quickly, the spike in tumblr tagging circa September 2015 may have been related to the strip about Lardo’s art show? I know that was a more Lardo/Shitty comic but it inspired a lot of Bitty & Lardo friendship fic and inevitably some zimbits as well.
As for earlier AO3 spikes… Feb/Mar 2015 was when people were receiving the Huddle zines they got as Kickstarter perks so that may have had an impact. Also there was a strip about Parse. There’s another spike in December 2014, probably Yuletide related, but also this:
And this: http://omgcheckplease.tumblr.com/post/106126040102
SO basically: PINING.
Edit: see further info in the comments about the Sept 2015 spike -- it was also apparently the first update in ages.