I would like to see a DLC where you're character discovers a pre-apocalypse storage container full of plant and animal DNA samples. I know this sounds like a doomsday movie cliche, but that's kinda why I want it.

And then what?

Well, seed vaults are a real thing, also called seed banks. Could actually make for an interesting object to search for in a DLC - a great Pre-War treasure that brings a lot of potential to the wasteland, with a lot of people fighting over it and even what to do with it. Could give us the choice to destroy it, too.

But it boils down to 4 options, the yes, the informative yes, the sarcastic yes, or the charismatic yes.

If you haven't destroyed the institute imagine how much fun you could have! All those weird and wacky animals wandering the wastes. Although it would be a nightmare for the Devs to model all those animals.

and then we do something cool with it

You can have pre-war cows at your settlements. It seems like a harmless novelty and it really boosts settler happiness, at first, but unfortunately it turns out that Deathclaws are actually a neotenic https://en.wikipedia.org/wiki/Neoteny species and eating a pre-war cow is what make them metamprph into their advlt form.

So basically, a GECK?

I like the idea of finding something similar to a Noah's Ark though. Sure, it's been done in countless movies and stories, but I'm sure it'd be interesting in the Fallout universe. Maybe the work of a humanitarian before Vault-Tec science created the GECKs.

When I first read the title of this topic, my first thought was actually Rage's Arks LOL.

regardless of which faction you side with. this would be a huge boon. especially for the institute

Institute: This will greatly help our research!

Brotherhood: We must obtain it for our scientists, no one else can have it!

Railroad: I guess..the doctor could have some fun with it?

Minutemen: Help, someone's stolen one of our pre-war flowers! You need to get it back!

Mhhh I'd rather go in a similar direction as Brink, that way you can have an actual story attached to it and you can change the destiny of the "Ark" by choosing sides.

https://en.wikipedia.org/wiki/Brink_%28video_game%29

It's a shame it was so under appreciated, it was a fun shooter.

Van Buren actually had a concept similar to this with the nursery at technologically advanced nature preserve hidden in a canyon. One of the buildings in it had sperm and egg samples of unmutated pre ear animals and an artificial womb to grow them in as well as a g.e.c.k manufacturing facility.