Just completed porting over for a custom IK node. If you have your own AnimGraphNode, the selection/widget/editing has moved from being part of the AnimGraphNode to being in a separate class derived from FAnimNodeEditMode.
Mostly it is a case of adding a new class derived from FAnimNodeEditMode - most of the functionality that is depreciated in 4.14 on the AnimGraphNode moves across.
Your FAnimNodeEditMode derived class has to be registered - the built in ones are registered in AnimGraphModule.cpp
I found TwoBoneIkEditMode.cpp/h gave the best example in my case for how things are now - I’d used it as a reference when I first wrote the code.