We have entered it around 15 years ago, when the majority of custom embedded architectures started to be replaced with ARM cores (around the ARM7 timeframe) and

We have entered it around 15 years ago, when the majority of custom embedded architectures started to be replaced with ARM cores (around the ARM7 timeframe) and when ARM application processores (ARM9, Cortex A) first showed up. The current transition is more about some more PCs and servers also considering to use ARM. I don't think x86 is dead. As long as x86 CPU manufacturers can keep up on pricing, performance and power consumption it will stay alive. And there's a lot more to that race than just the instruction set. Intel had a lot of weak years, but AMD showed that x86 doesn't have to stagnate.