The proposal is needlessly complex. First plus a prospect is probably what he will go for as a rental. Throw the rest out. If the Leafs were interested they could deal with the cap implications elsewhere. It doesn't have to be all one trade. FWIW, I don't see retention on rentals as a huge game changer. It opens up the market a bit, but it's more like, if you get an offer you like, you retain to make it work if needed.
I'm torn on whether the Leafs go for a big dick rental this season. On one hand, they've got to prove something before you keep wasting assets. On the other, in for a penny in for a pound, I guess. I would way rather go big on a guy like Forsberg than spend another 1st on a ~30 point defensive winger to play on our top offensive line...