logind should tell us why hibernation isn't available:
- hardware not supported
- insufficient swap
This would be used to show the user why hibernation isn't an option.
We generally provide an answer now:
$ sudo systemctl hibernate
Failed to hibernate system via logind: Not enough swap space for hibernation
For further enhancements, please open an issue on the new bugtracker on https://github.com/systemd/systemd/issues/.