So, I checked around. The only notebook editor in IJ that I’m aware of is the one bundled into PyCharm. And although it is probably possible to make it run with the kotlin kernel, the PyCharm itself doesn’t have kotlin support, so you’ll not get any coding help from it.
It is theoretically possible to extract this notebook editor into separate IJ plugin, but so far we have no plans about it.
If this is something important for you, we can create an issue in the youtrack and see how popular the request and what we can do about it.