So preferably this will be used by people who have read all the current ‘Who We Become’ stories and will try and predict relevant stuff in the future / past that is not yet revealed (past because of the slightly eccentric timetime of events relative to stories being released).

SPOILERS AHEAD!!!

Changelling threat.

Having the changellings around as they are in current Who We Become may simply lead to nothing.
It may be that it was just a tool to keep the EQG counterparts confined to the castle and also showcase the difference in how sunset and twilight think through a problem and react to Celestia telling them about the threat.

We have little to go on, the canterlot wedding (probably) played out as it did in the show but of course thorax isn’t the new ruler and there is no peace between ponies and changellings like there is in the series. That leaves Chrysalis and her hive still with the desire to feed off the love in equestria.

Sunset Shimmer summarised that the latest plot from Chrysalis is intended to lead the equestrian citizens into panic and mistrust of there own neighbors by putting spies in every city in equestria (and have them be purposely found out?).

And I can’t help but suspect Celestia.
Maybe to put off a war she made a deal whereby a small number of changellings are allowed into equestria to feed off love and return it too the hive.

It sounds weird as Celestia surely would find a better way of protecting her little ponies.
But maybe she’s scared of Chrysalis as she was actually able to defeat her one on one.

Or maybe it will lead to more sensible, probable and character conforming drama.
Or nothing at all.

But hey that just a theory.

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So I'm super late to noticing this I love this theory though, it makes me really happy to see people coming up with ideas about what will happen in the series

Without confirming or denying anything substantial, I will say that there are absolutely plans for the changelings. They were introduced a bit too early because I misjudged how many stories I was going to be writing, but they'll play a major part of the series eventually. I'll also confirm that Canterlot Wedding happened exactly as it did in the show.