Brock vs Lashley is the most important one they need to do and it needs to be done sooner rather than later while Lashley is on the streak he's on and killing it.
The fact Bob vs Brock hasn't happened yet
It should have been Brock instead of Goldberg. I'd say we could get it at Survivor Series if Brock won the belt as they'd be forced to collide, but I have no idea how much longer Lashley is going to hold it.
You'd ideally want to do it whilst he's champion because it'll feel like a much bigger deal. Wasn't much hype before because he wasn't built up like he is now.