I am sure that Federation ship that went missing a couple of months ago is in the Thargoid universe right now. An alternative theory (from another thread I was reading) is that Thargoids have already invaded, but are just playing in another instance.
Hah! Funny you should say this, I was just wondering the same thing - about how the Thargoid invasion would work.
Imagine some intrepid explorer - Erimus? Or future president Murp? - posting here: "Attention all Cmdrs! I've been attacked. Thargoids! They're following me from system to system.. I need help, meet me in the shadow of NGC 7822. Oh, and if you're not sure, I'll be the Asp with a billion Thargoids on my tail".
Cue a massive rush of combat-equipped explorers rushing out to face the enemy. A massive flotilla of combatty Asps, Anacondas and Diamondback Scouts. And then, suddenly.... nothing happens.
"Uhhh, guys? There are 32 of us in this instance. Someone has to leave to let the Thargoids in!"
"I'm not going, I was here first..."
"I fly a Conda, I leave for no man..."
"Me neither, and drop 10 Gold for suggesting that I should!"
"Why did the groigan dance?"
And so, the great, second Human v Thargoid War was averted, with Man and Thargoid in the same system but stranded in separate instances, trading strongly worded insults about each others' mother(s).