ihlar

Sure, the spin bit allows for buffer bloat detection, just like icmp ping does when used actively. Just like stated in the material you share, the best way to mitigate this issue is to remove bufferbloat in the network. There are great easy to configure AQMs nowadays, and servers can do their part by using congestion control algorithms that are less prone to cause excessive buffering e.g Googles BBR.

Indeed. But it will still expose its initial handshake RTT.

Even without the spin bit it is possible to obtain at least one RTT sample per observed connection, simply by observing the initial handshake, the spin bit doesn't add any meaningful information from a location perspective. An endpoint that wants to obfuscate its location could simply add a bit of artificial jitter. Here's a paper by Brian Trammell where he investigates how well RTT information can be used for geolocation: https://github.com/britram/trilateration/blob/master/paper.i...