So, in the Force and Destiny campaign I'm running, we just finished up our Prologue - essentially the adventures from the Core Rulebook and GM Kit - and now we are jumping into the main story of the campaign itself.

The Prologue served to introduce the PCs - Jed Exiles who survived the Purge - to one another, while also allowing the one Exile who hadn't yet built a lightsaber to acquire one through the adventures. However, it is also meant to introduce the two campaign antagonists, both Imperial Inquisitors. I was going to have them simply show up towards the end of the next story chapter, but now I'm debating teasing them with a little Prologue stinger, if you will. It would essentially be a short write-up that introduces them, though not naming them or anything too revealing.

Has anyone done anything like this before? Good idea, or should I just wait to have them show up in-session?

I'd drop hints in-game for smart players to pick up on. Maybe there's a beggar who vanishes for extended periods, and when the players investigate, they find that he's an informant for one of the Inquisitors. Don't do this too often though, or the players might stalk anyone who does anything out of the ordinary until they find the "link" to the Inquisitor

You could have an Inquisitor make a speech in front of a large crowd the PC's are a part of. they can see his malicious intent by reading between the lines, but can do nothing about him, it could set in motion a 'witch hunt' for expected force users.

I always love to put in foreshadowing. In the first session I had with my new group last week a successful perception check showed them they were being followed by a spy working for an antagonist from one PC's past, who will end up being the big bad of the campaign. She actually shot the informant dead on the spot once they got the info they wanted. I was honestly so surprised I flipped a light side destiny to dark just for flavor, and come on that's pretty "dark". (To be honest the antagonist killed her parents ruthlessly, and she's more of a grizzled character so it made sense that she would kill him. It'll come back to bite her soon enough).

Plan ahead and give your group a likable, helpful NPC who befriends the group.

After a session or two of having bonds of friendship form, your antagonist appears and kills the NPC.

Be careful not to abuse this formula.

Have them hear rumours of a suspected Jedi working with a local crimelord, they turn up to investigate find the placed trashed showing signs of indiscriminate storm trooper blaster fire but the interior looks like someone tore it apart with either some kind of vibrosword some of which looks like it was thrown and other parts look like something picked up various bits of now crushed furniture to use as cover before smashing it done on their late contact with said crimelord.

Watch the Star Wars Rebels episode where Ahsoka turns up after the Inquisitors left everyone assuming they were dead as another example!

Plan ahead and give your group a likable, helpful NPC who befriends the group.

After a session or two of having bonds of friendship form, your antagonist appears and kills the NPC.

Be careful not to abuse this formula.

My favourite variation on this theme: the likeable, helpful NPC who befriends the group and turns out to be an antagonist.

Really usable only once though because they probably won't trust anyone for a while.

To the OP's questions: I haven't quite done anything like that as I recall, although I've written a couple of short stories to provide info on the background on some NPCs and maintain interest in the campaign during a long hiatus. Usually I'll try and throw some sort of tease in there, but that wasn't exactly the goal of them.

Personally I would probably be ok with such a write up, but I can see some people not being so. In that case, I'd default to SirSprinkles's suggestion of hints in game that they can hopefully pick up on.