Are we theorizing that both players (and both teams) want 8 year deals, and this deal is basically swapping the rights to offer an eighth year by agreeing to re-sign their own player before the swap, and both players going along with it because they crucially want that eighth year?
Because if not for that - I don’t see why this would happen. If either of them wants to test the ufa market and is willing to accept the best seven year contract the highest bidder in the market will offer, there’s no reason they’d have any value here. At the proposed trade time (next summer) they’d hold all the cards for a walk to free agency.