With colima I can run AMD64 (x86) Linux containers in my Arm64 too. I think this is strictly for Arm64 Linux VMs, or is there some way to run x86 with this too?

You can run amd64 binaries inside an aarch64 Linux virtual machine. Although they're not supporting Rosetta for macOS apps from macOS 27, the Rosetta support in Virtualization Framework will remain.

What’s the performance when you do that?

Rosetta should be supported

Not for long!

Very unlikely to lose support for Rosetta for Linux. Maybe just Rosetta 2 for mac apps.