Whats in it for washington?

Couple younger players and a pick for a guy they probably won't end up bringing back

It's an interesting proposition for Rust.
Nick Robertson is the obvious main attraction and has the lion's share of the value on TOR's end. (And now I want to see one of the Robos wearing the RoboPenguin jerseys, it'd be funny.)
Kerfoot's been a pretty consistent middle-six player for his career, but is probably closer to a 3rd liner than a 2nd. Fills in some of Rust's production in the short term.
Voit is currently the leading scorer in the OHL so he's really intriguing. Not sure where his ceiling is.

Ultimately, Rust took a very team-friendly deal in the offseason (at least in AAV) to stay in Pittsburgh and he's been an electric part of our offense for a few years. I don't know if the Penguins will be willing to move him, even if we end up selling at the deadline. And even if the team is willing, there's a NMC on the first 3 years of his contract and I doubt he'd waive it.
If it was close to the deadline and the Pens were basically out of the running, and Rust would waive his NMC, I think I'd accept.

Kokkonen has very little trade value and Hirvonen is a decent prospect.

Still doesn't make sense for Washington to trade one of their best defenceman away.

As a Penguins fan, I would not hesitate. What Pittsburgh needs is to get younger, get some futures. This offer provides that, and we'd still be competitive. It definitely makes a lot of sense.