My wife just got the Carbon 6th gen. There is an ACPI patch to restore S3. See https://delta-xi.net/#056. Once you've got the patched dsdt.aml, I highly recommend not following their directions, and just loading the file in grub by creating /boot/grub/custom.cfg with the line:

acpi patched_dsdt.aml

This has the advantage of not requiring any manual intervention every time your kernel is updated. The downside is that if you try to dual boot W10, it will BSOD on boot with an ACPI error. To overcome this, take the original dsdt.aml and load it in a custom (not auto-probed) menu entry for windows. You can just clone the auto-probed line, and add before the chainloader line:

acpi old_dsdt.aml