The trick with deals for young players is this. If you're on the upswing towards a window of competitiveness, you sign for term at the expense of immediate cap space because on the upswing you don't need it, but you will later. If you're solidly in your window you go short to reduce cap and stay in that window as long as you can and hope for the best once it comes time to pay them. So teams like the Wings, Buffalo, Ottawa, etc... lock in kids now and teams like Colorado, Florida, Edmonton, Vegas will be trying to reduce immediate cap hit as much as is possible. Bridging Mo or Ray for 3-4 years wouldn't be wise because you don't want a big raise right when you should be looking to add the final pieces.
If you f*** up on the valuation it really doesn't matter if it's 4 years or 8 years, you f***ed up anyway. The Kings just proved that no contract is impossible to move.