I think Herb Sutter and Bjarne Stroustrup where against it. Its like a glorified ifdef. Its too low level a solution. Concepts solves the same problem in a higher level manner.

Edit:

https://isocpp.org/files/papers/n3613.pdf

"In this paper we consider the impact and risks of adopting static if. Some of the problems addressed by the proposed feature are real and urgent, but on balance this proposal this proposal would do much more harm than good. Language features addressing these problems must not negatively affect the language and our ability to build tools around it. We conclude that future development of static if should be abandoned, and that alternatives such as “concepts-lite” approach should be pursued instead."