Sander Stad wants to use Powershell workflows to back up databases in parallel:
It’s possible to use a workflow to execute your backups. You have to take into consideration that there is a downside. If you execute all the backups at once you’ll probably get issues with throughput if you’re dependent on a slow network for example.
You could always add another parameter to filter out specific databases to make sure you execute it as a specific set.
Sander does include his script, so check that out.