Ok, but then what he's doing?
Imu killed his mythcial ancestor, "killed" his father and his clan, Teach himself wants to be King of the world and has probably the fruit wanted by Xebec.
What he's going to do?
Well he's heading for the One Piece. He's collecting rubbings of the poneglyph's, he's collected Pudding to read them. So clearly he thinks going there is an important step towards Imu.
I just don't see what Teach has to offer. Most fan theories state he either solo's the world gov, which is getting less and less likely (already a 1% chance before Imu was revealed) seeing what powers the Knights of God can be pushed to. Or that he's going to be a bait and switch villain after Luffy defeats Imu.
My issue with idea #1 is that Teach and his crew are laughable compared to the WG. They likewise do not represent the centuries of oppression Whitebeard spoke of coming to light in the final war. They did not cause it and have nothing to do with it besides being victims of this oppression. So Teach taking out Imu kneecaps a lot of what Oda's been building towards.
Idea #2 is just a shallow bait and switch IMO. It's really not appealing to anyone but BB fans.