Why not go for C++17 already? C++14 seems pretty arbitrary, AFAIK C++17 is already supported by GCC, clang and MSVC fully [0]. It's also now the default dialect in a few compilers including GCC. Meanwhile C++20 isn't really well supported at all in the moment [1] so it makes sense waiting more for it, even though features such as Concepts and Modules should simplify library code a lot and make some tasks much more trivial.
The argument I can see is that 14 is the minimum feature set that every engineer knows how to use, and before 14 you are missing some of the "core" features of the language that are widely used today. By contrast, some things in 17 are still foreign to some engineers, although there are no real "breaking" changes from 14 to 17 (in terms of the model of how to think about the language). 20 and 23 are a bit of a mess in terms of support.