Earlier quoted context omitted.
What does it mean to be "in Linus' tree" if it's already on Linux and everywhere else? Like it will be built in somehow?
Right now, it is not part of the Linux kernel. It is just some random external software that you have you download and compile yourself against the source headers of the kernel you're currently running. It got merged into the net-next tree, which meant it has been approved by the maintainer of the Linux kernel net branch to be included into the kernel. Linus has now pulled it from net-next into his own tree, which me…
That's not the important point.
The point being, when merged as part of the kernel officially, you know it will get more support and eyes for stability and development power as the kernel wouldn't want to ship anything that's at some unstable state.
So you can expect long term usage and maybe RedHat might pick it up as its official VPN solution instead of libreswan some day.