The bottom layer of C4 is still basically UML, although everyone usually skips that.

I love IcePanel and would recommend everyone try it. But like all these things, it requires an almost superhuman level of commitment to get value out of it. It has built in mechanisms to keep you honest and up to date and I have found it useful both the strategic and tactical level when used right. But ultimately it’s difficult to build an engineering culture around long-term, living diagrams. The moment everything gets out of sync it might as well just be a photo of a whiteboard. I strongly suspect this sort of platform plus AI will be a great combination (I think at least one HNer is working on exactly that and I assume IcePanel too).