The Linux kernel developers hate their solution, and they only used it because they can't think of a better one. It causes enormous increases in complexity and kills performance in many cases.
They revived previous work on this as part of the KAISER work in November 2017, and still had major bugs with it in February 2018 (ie, 4 months later). That's pretty similar to the 6 month timeline mentioned here.
https://lwn.net/Articles/738975/
https://arstechnica.com/gadgets/2018/01/whats-behind-the-int...