This is really inner API, I really don't know why it was exposed as configurable in the first place. The changes are necessary to implement a lot of the Hot Rod client improvements coming up in Infinispan 7.0.
Indeed exposing the transport factory is something quite internal and shouldn't have been done in the first place. I don't expect people to extend it - in fact that interface has been changed in 6.2 as well, without any concerns - but for now would be a bit risky to remove it entirely. Let's keep it there just in case - trying to keep backward compatibility in this case is a significant effort and not worth making.
Probably needs to be documented in release notes. Adding the flag.
This was documented in the 6.3.0 Release Notes. Since this was closed NOTABUG, I'll assume we don't want this documented for any other release's Release Notes, hence removing the flag.