Dynamic dispatch adds headaches to the build process; they are surmountable for sure, but in my experience the build wrangling to make it all happen is harder than the original work of rewriting your code with intrinsics!

The other major problem I have with dynamic dispatch, at least for the SIMD code I've written, is that you have to do so at a fairly high level of granularity. Most optimized routines are doing as much fusion & cache tiling as possible and so the dispatch has to happen at the level of the higher-level function rather than the more array-op-like components within it. And mostly, that means you've written your (often quite complicated) procedure several times uniquely instead of simply accelerating components within it.

I have not used Highway - if it dramatically simplifies the above, that's excellent!