I was very excited about Oklab, since the day I learnt about it. There are four areas I can think of where oklab can be useful in krita. First is of course a dedicated colorspace for a layer or entire image, but I dont see myself using it.
Secondly, as mentioned by some users above, a normal blending mode utilizing oklab. This can be immensely useful while still retaining the image in srgb colorspace (which has its advantages too).
Thirdly, in some of the filters, like curves, where we already get options like lightness and saturation in addition to the usual RGBA.
And last but not least, and an OkLCH based color picker, which as others mentioned, is merely a polar form of OkLab. However on this note, I already implemented such a color picker and has been using it for a long time now.
This color picker allows me to change color based on either keeping hue constant (left side) or the value constant (right side), hue and value being in oklch terms (hue=h, value=L). The problem is that I wrote this addon in a way which assumes lots of things available on my own system and not easily portable or installable. There were some issues like numpy python library not available for the python krita is using, so I had to manually fix it.
Other than that, its a straight up implementation of the code described by Björn Ottosson (creator of oklab and oklch) on his blog, just using python numpy code. If anybody wants I can share the relevant source for this (its part of a larger addon which I implemented with many little features), but again, I dont know how hard/easy it will be to use on your krita installation on your platform/machine.