Thinking on it now, I'm really sad the Drell don't have their own ark.

They're a species in the verge of extinction. A drell ark would make no sense. A drell Pathfinder, working on behalf of both Drell and Hanar, would be cool.

Are there even 20000 Drell? All that's left of them are on the Hanar homeworld, right? Or do they still have some left on their planet?

There is also no rule that says that there won't be a Drell pathfinder aboard the Quarian Ark. The Drell and Hanar should be in charge of their own future in Andromeda, and for that they need a pathfinder.

We're assuming the Quarian and co. Ark is the same size as the previous arks. Wouldn't more species on the same ark maybe imply a bigger ark?

How many people do you need for a viable breeding population anyway

Are the drell coming because they want to or because they kind of have to?

Drell needed an arid, dry climate to survive, so it seems like Eos and Elaaden would actually be perfect for them. Maybe they'll actually bounce back in Andromeda. Seems like there's actually more habitable space for them than in the Milky Way.

No Krogan pathfinder.

I think they've paid their collective debt. If they want to survive as a species, they must not "move-in" with the hanar on New Kahje. They need a new world, apart from the hanar.

They could use the, "We underwent genetic engineering during 630+ years of cryo, so we can tolerate high humidity, now". That would be weak, though; and it would leave them in service to the hanar, as you said. The drell need a fresh start as badly as the krogan.

Yeah, I thought of them almost immediately when adventuring on Elaaden!

It would be cool, but I doubt they'd do it. Quarian fans crave fan service; and they'd complain if even one potential quarian was replaced by a non-quarian. It would probably be especially fierce if they didn't get their quarian Pathfinder. I do like the idea, though.