Google BBR seems to used the same exponential probing that slow start does, so I wonder how it will perform when you are staying in network and don't often have to worry about packet loss or congestion and want the link to start off at full throttle.
Once BBR enters its steady state it intentionally cycles faster and slower, but this seems like it is creating additional latency when you don't want it. Think of a traffic burst that happens just as the link decides to cycle slower.
It also seems like the protocol intentionally runs slower that possible as to not create buffer pressure on the receiving side, if I'm understanding this quick description properly: "then cruising at the estimated bandwidth to utilize the pipe without creating excess queue".
The this line just scares me: "Occasionally, on an as-needed basis, it sends significantly slower to probe for RTT (PROBE_RTT mode).
Google is going to make patches that work for them, but that doesn't always mean it will work for everybody else. This seems very close tailed to Google's traffic issues and serving HTTP over persistent connections, and not a general purpose feature, think of games, intranetwork low-latency applications, etc.