I sponsored implementing the client side for FreeBSD when I worked at a large service provider. The use is cleaner when you have control of both ends, such as

I sponsored implementing the client side for FreeBSD when I worked at a large service provider. The use is cleaner when you have control of both ends, such as a cache/proxy to origin or peer cache and you aren't going to be subject to packet manglers and can configure a shared cookie out of band. The typical microservices misarchitecture would really benefit from this kind of thing since the setup time of TCP is substantial. We did have some ambitions to expose TFO to customers in some way but unfortunately I left before that ever went under test to see how it could be commercialized.