You should give Dear ImGui (which is mentioned in the article) a try. I was reluctant myself when I discovered it a couple of years ago, but it is such a joy to work with and so "obviously" the right thing on a very basic level that ImGui is now my default choice for writing UI tools (even with the disadvantage of not having a native look and feel).

It's still possible to put a data layer on top of immediate mode UIs, which basically turn a data representation into a sequence of function calls. But I think this would bring event handling back, which defeats the whole idea of an immediate mode UI :)