Don't get me wrong, I love Teach, I just don't see him has this grand emotional final antagonist. The most epic? The most entertaining? For sure. I just think this manga begins and ends with Shanks, hence why he's featured in every volume ToC with Luffy and his crew. Plus I feel like this is where Zoro would fight Mihawk, considering his relationship to Shanks. Usopp meeting and surpassing his father just sounds like endgame material rather than Van Auger imo.
Idk, we'll certainly see how it goes!