I haven’t tried it yet, but this looks promising:
So far, this is the only alternative I could find that has a free version, works on Window/Mac, and works with most printers.
Another option is setting up a folder that is monitored for new files, and printing them as they are added.
You can install Google Drive, OneDrive or Dropbox, and use a workflow to save attachments to a folder that will be synced to your Mac/PC.
Then, you just need a program or script that prints new files when they are added to a local folder. This simplifies the requirements and opens up lots of options.
The exact solution would depend on your OS, coding skills, number of users/devices involved, etc. But it’s much easier to find or write a program to auto-print files from a local folder, than to write a cloud-printing solution.
So just consider your hardware and user case, then look for a way to auto-print local files and combine that with a cloud sync.