Yes, we all (I think) agree that scripture supports that Christ NEVER sinned, as He is the faithful High Priest. However, "if" you take away the possibility that Christ could have sinned (like Sproul is stating) then once again you have fallen into the abyss of no actual temptation ever having taking place in the life of Christ.... Sproul is IMO correctly splitting the hairs of could have sinned and would have sinned. Christ has never and will never sin, however, in His humanity He could have sinned before His glorified state.... though He never would... for He is the God-man...

Reformed and Always Reforming,