To me, I don’t see why not either. Others may see your or my ideas as hare-brained, but can anyone really put that label objectively on the items in current NFL GM rules playbook, before they got ratified? Maybe some people saw trading compensatory draft picks as dumb, before it became allowed.
The GM is making a bet that the player(s) bring in more wins than they give to the other team. If I think that Deshaun Watson can bring my team an extra 3 wins a year, and the Texans are willing to trade Watson for 2 wins a year, I’d take that deal in a heartbeat.
In a sense then the OP’s idea has already been implemented and this has always been a part of football. The OP is just wanting to raise the cap above 0.