I like Marco Rossi as a prospect. A lot. He's my #4 after Laf, Stutzle, and Drysdale on my board.
That said, I wouldn't trade DeAngelo for him. Winning the Lafreniere sweepstakes is going to accelerate things. The Rangers wouldn't have traded a 2nd rounder to get Staal off the books and wouldn't have bought out Lundqvist if the front office didn't think this team could make noise this coming season.
If DeAngelo gets dealt, it's going to be for another quality player rather than a future asset. Gorton is setting up for this team to contend now and for the duration of Lafreniere's ELC. Things will get hairy in two to three years when Kravtsov, Kakko, Lafreniere, Zibanejad, Fox, and Shesterkin are all going to be due new contracts if they perform to our hopes.
The best move with DeAngelo is to bridge him two more years to still keep him an RFA after the bridge deal or to trade him this summer for a top 4 LHD or top 6 center. His value very well may never be higher. Reading the tea leaves, the latter may be more likely than some may think.
Maloney was gushing about Lundkvist yesterday on the radio. The Rangers see him as a plug and play top 4 NHL defenseman once he signs. He's not getting dealt for anything short of a Godfather offer, I don't think. DeAngelo is the guy that makes the most sense to deal to upgrade elsewhere.