Weevil said he's going after Luffy IIRC but he's also after Blackbeard too. Idk where he'll fit into the story and what his role is but I had hoped for a mini arc where the SHs go to Sphinx island where I think Ace and WBs Graves are too and Luffy can fight Weevil there and sort out Weevil from having the wrong idea this whole time.
Idk why Weevil was introduced honestly. An editor or someone else said, once Oda explained his intentions for Weevil, Weevil audience became really cool at least. Sounds like another Senor Pink, subverting expectations/initial judgements scenario or so.
Oda has some weird hate boner for the WB pirates. We don't know why Croc wanted to kill WB too but we can try to guess why.