monotonic spline interpolations in Darktable

I just read part of the thread and I’m wondering what kind of solution would be better ?

Find a new interpolation method that preserves the monotonicity
Keep the current interpolation with all the good of it (implemented, tested and probably fast), but change the UI interface to automatically raise/lower the points in the neighbourhood to avoid the monotonicity problem ?

I have the feeling that the second option could be easier from a development point of view (Although, it could take time get right)