Does it not dawn on you writing that, that the importance of finding the One Piece is yet another reason why it's obvious Imu isn't the final villain?
Oda has spent many years developing Blackbeard into one of the most iconic, compelling villains in the history of the medium, and he's done it without every tipping his hand. Nearly 1200 chapters in and we don't know much but we keep getting hints,
Egghead revealed the Gorosei know something about teach. Vegapunk's comments on the D Clan seemed to call back on WB's final words to Teach.
Teach is somehow connected to Rocks, who in his own way was connected to Imu, if no other reason than trying to usurp him.
Blackbeard is so obviously the final villain and he should be.