In a previous Apple press release[1] they said:
> The Mac is now one year into its two-year transition to Apple silicon, and M1 Pro and M1 Max represent another huge step forward. These are the most powerful and capable chips Apple has ever created, and together with M1, they form a family of chips that lead the industry in performance, custom technologies, and power efficiency.
I think it is just as likely that they mean "completes the family [as it stands today]" as they do "completes the family [permanently]."
[1] https://www.apple.com/newsroom/2021/10/introducing-m1-pro-an...
edit:
This comment around SoC code names is worth a look too: https://news.ycombinator.com/item?id=30605713