Luffy talking about physically wanting to beat Shanks is actual foreshadowing, because it's been talked about many times in this manga and is one of Luffy's top goals.
I agree with this part, I also think that Luffy vs Shanks is going to happen, although I don't know in which format. The fact that Luffy says that he's going to defeat all 4 Emperors but shows only 3 fingers, means that Luffy has his own way of dealing with Shanks. I personally think that Luffy wants to have a "duel" with Shanks–something like Zoro vs Mihawk–to find out who is the strongest. Plus, I think Luffy's crew will fallow Luffy's steps and have duels with Shanks' crew.
Guys, this hasn't really been foreshadowed. Shanks was ready to fight literally everyone that arc, including Marines. He then looks at Teach and warns him too. All Teach says, "it's too early to be fighting with you". That's it. Nothing indicates there's this massive foreshadowed battle that will occur between Teach and Shanks.
I disagree with this part for multiple reasons: 1. Shanks has a "
VERY" visible scar on his face left by none other than Blackbeard himself. Scares are "
VERY" important in one piece; Whitebeard's huge scar in his chest was left by someone who was clearly his enemy, Luffy's scar was left by Akainu who was trying to kill him, Kaido's scar was left by Oden who was also trying to kill him etc. Shanks' scar has the same meaning, their conflict (for whatever reason) hasn't been solved yet, which means that their final show down has yet to happen. 2. Blackbeard and Shanks are clearly enemies; Blackbeard essentially killed his captain's son by giving him to the Marines, Blackbeard also tried to kill/capture Luffy too. 3. And third but not least, Blackbeard has to–and probably wants to–take down all Emperors for his goals, which means that at some point Shanks and Blackbeard, one way or the other, will fight, with one of them eventually dieing–and since Blackbeard has to fight against Luffy later on, means that Shanks will be the one to lose, unless you think Blackbeard doesn't kill his enemies like Luffy.
If all of this still doesn't change your mind, then I guess we'll agree to disagree.