I find it interesting that half of the comments indicate that people don't really understand why this would be needed and the other half are surprised that is hasn't been offered before.

Personally, I'm in the first camp. I'm used to taking instances for granted on the rare occasion that a low-level issue arises and just promoting a replica or trashing it if it's stateless.

I'm assuming the use case where you care about fixing the type of issues this feature helps debug is fairly esoteric?

Proxmox has had this for quite a while.

https://pve.proxmox.com/wiki/Serial_Terminal