It makes me uncomfortable that this mandate is coming from a Canonical employee. After all, if this switch was a good idea on merit alone, it would happen organically without requiring this kind of combative communication.
What's the long-term play for Canonical here?
Apt has just 3 listed maintainers, and judging by the git history this guy does 90% of the work. Him making the decision _is_ it happening organically.
Open source fundamentally is a do-ocracy (it's in literally all of the licenses). Those who do, decide; and more and more often those who do are just one or two people for a tool used by millions.
It's hard to imagine their is some malicious financial incentive to choosing a different language to write the package manager with...
The obvious potential motivations are things like making a more reliable product, or making their employees more productive by giving them access to modern tools... I guess I could imagine preparing for some sort of compliance/legal/regulatory battle where it's important to move towards memory safe tooling but even there I rather imagine that microsoft is better placed to say that they are and any move on canonical's part would be defensive.
"What's the long-term play for Canonical here?"
Presumably it's rewriting critical parsing code in APT to a memory-safe language.
The long term play is to drive out community participation and bring in corporate control in the apt/Debian ecosystem.