They already have, Ellsbury and McCann were both qualified FAs. GRanderson was too but the mets first round pick was protected so the mets would lose this second round pick, and the Yankees would gain a 1st round comp pick.
So far though, since the Yankees have signed 2 qualifying FAs, the would lose their first rounder and their first round comp pick, while keeping their second rounder, unless of course they sign another qualified FA, in which case they'd lose that too.