Obviously a 1st would be ideal, but maybe 2 2nd's is more realistic. Considering the value a capable RHD carries along with his contract, there should be no shortage of suitors so I could be undervaluing him. Still, I'm not going to be a homer and suggest something stupid.
As for a cap dump, a lot depends on this offseason. Leddy looks like he's on the chopping block in order to free up space to sign Barzal, Pulock, and Toews. Pelech, Sorokin and Beauvillier are up for new deals after next season too. Boychuk, Clutterbuck, Leo, and Hickey all would be in their last contract seasons in 2021-22 so they gum up the works if they can't be moved. There is also Ladd who is pretty unmovable. Lou might be able to pull some Hossa like shenanigans on them though to get rid of them. Cizikas is also a pending UFA next season and would have plenty of suitors if made available now.
In short, taking on a cap dump is unlikely and the roster is already overloaded. Bellows, Wahlstrom, Koivula, and Holmström will need roster spots next season and in 2021-22. The defense and goaltending is set up for the long haul so no real openings there.
Draft picks only make the most sense for Mayfield.