What is the official rating threshold that Uber will deactivate a driver at?

The threshold varies by market.  It is a well established fact that certain geographies rate more liberally or more conservatively and thus there is no single number for the entire US.  However the long standing number for reference and concern is 4.65  and we can assume once you see any version of 4.xx you should be mildly concerned.

Generally, the threshold is 4.65   

Unless you're actively trying to be deactivated, that shouldn't be hard to avoid.  

I have actually read that this number varies by location, hence the confusion.

Riders have 30 days to rate driver. What I found really interesting is Riders can change a drivers rating at anytime (at least 7 mths later) probably longer. Dont know why this would even be an option. I also dont think anyone would go back that long ago to do so but why even give that option? 

It's honestly quite hard to get your rating that low. You would almost have to try to get deactivated.

I think the official number is actually 4.64.

I think it is 4.6? At least that is the last I knew so unless they have changed it recently.