What's the criterion for a full departure?
RDNA1 made the effort to move parts of its ISA back console-era encodings, when the nearest GPU to depart from was Vega. AMD still seems concerned with some level of compatibility with GCN, so I haven't seen the claim that Navi 2x is changing this.
I'm not sure a full departure is an optimal solution in the face of backwards compatibility.
Sony would have the most examples of struggling with significant architectural discontinuities, such as the Cell to x86 transition, which I'd argue is at a minimum a large if not full departure.
New?
Perhaps it is time...
https://forum.beyond3d.com/posts/711822/