I would love some bigger enemies. Could do a mirelurk queen behemoth. imagine taking on this massive hulking thing that looks like a small island from a distance, suddenly, it moves and comes out of the sea off the coast of the Castle. It becomes larger and larger as it gets close and your only option is a massive artillery barrage and Fat Men. After a grueling battle, you finally take her down, and you gain 3-5 legendary weapons from her along with a bunch of materials.
Also, a quest where you have to take on a legendary Alpha Deathclaw behemoth. You have to take a wing of vertibirds to stop it.