Are we going to have Split in platform where developers is expected to debug on both Arch? This isn't the same as moving from PowerPC to x86, where majority of Pro Apps are already on WinTel. ARM is still relatively new on many Pro Apps. Adobe may be slightly better equipped, but not AutoDesk.
If not, would Apple spend additional hundreds of millions on 100W+ CPU design that are sold in tiny quantities?
It is also worth pointing out Mark Gurman has been saying this since before he joined Bloomberg when he was at 9to5Mac. And since 2016 when he joined Bloomberg the rumours were taken more seriously.
And the first rumours to suggest Apple is working on ARM Mac goes back as far as 2010.