It would be interesting if BB becomes PK first then Luffy takes it ngl.
I can see the temptation for wanting this, but that effectively ruins the race to PK and the themes behind it. Like imagine Whitebeard's "its not you" speech not mattering because Teach found One Piece first.
Im not going to deny Blackbeard cant or wont be relevant to the island, in fact I actually think he makes it there like Luffy, but imo this is why I expect him to lose before Luffy actually becomes Pirate King.
Right now, my "personal" expectation following Elbaph involves the war for the 4th RP between the Yonko and likely Marines. The fallout of this leads to Shanks dying to Teach and possibly Akainu losing to Luffy. That follows to both the BBP and SHP making it to LT and fighting over One Piece.
The real question is however if Imu is going to be relevant at that exact moment or we actually go backwards to Mariejoa due to the Galleila, Noah and the FI prophecy. Imu losing anytime before this makes little sense since he's literally the main plot resolution of finding OP
Edit: Its actually why the Blackbeard fanbase seems to think Teach can take out Imu before finding One Piece, because they know it doesnt make sense if he actually becomes Pirate King before Luffy. But becoming PK is literally the stepping stone to either controlling everything or liberating it all so you can see why the idea is just absolutely backwards.