Well i think BB really needs a huge power up to be able to put a fight against Shanks at least right now. i say that based on the fact that Shanks destroyed Kid's crew in one attack while BB has some of his crew , was injured by Law and had to work really hard even when he had the advantage that Law has a DF , while he can neutralize the DF taking a huge part of his opponent power. he will not have this advantage against Shanks , and i think we can say for sure that BB cannot see the future at least if he could Law will not cause him problems.
I think Shanks will give him a DF awakening maybe for his 2 DF , only then he can beat Shanks lol