They have been hyped as rivals since the Baratie and WB speech to Shanks. If Oda will ever make them fight it will be an extreme diff either way.
But anyway what really matters is that Shanks is the role model of Luffy, the Jesus MC Oda loves and put before everything, how can the mentor of Zoro be put before the mentor of Luffy. Anyway time will tell, I could also be wrong but I doubt it (how many times has the mentor of the MC put below somebody who is not the final villain or the MC himself in manga history? It usually doesn't happen).