I have just added a new PR: https://github.com/numpy/numpy/pull/4244
From the commit message:
This PR replaces the generic binary search functions used by `searchsorted` with type specific ones for numeric types. This results in a speed-up of calls to `searchsorted` which is highly dependent on the size of the 'haystack' and the 'needle', with typical values for large enough needles in the 1.5x - 3.0x for direct searches (i.e. without a sorter argument) and 1.2x - 2.0x for indirect searches. A summary benchmark on float and int arrays can be found here.
Furthermore, the type specific binary search functions can take strided inputs for all their arguments, which is a step in the right direction to eventually add an axis argument to`searchsorted`.
Any comments and reviews are more than welcome!