I just would like to point out that that issue is not about a specific CPU, but about the very architecture of the M series itself. It's almost impossible to avoid the bug without greatly sacrificing performance.I didn't read too much into the security bug in the M1-M3, but it makes sense as to why they would skip it for the higher end models rather than ship them with a flawed CPU.
That is, as far as I understood it.
I'm still waiting to know what they're doing about this.