To increase the security, SSH key support for the ftp remote backup storage would be a great feature. Also, please consider to add S3 compatible backups.

There is no option to encrypt backups. I do not trust Google or any other cloud service. Yet I could use the (otherwise completely useless) storage to put my backups there.

So please include a proper and secure encryption. Thanks!

Edit:
It could be as easy as running gpg as a last step before uploading:

Encrypting (simple tar example):
tar -czf - [FOLDERS] | gpg -c --batch --passphrase [PASSWORD] -o backup.tgz.gpg

Decrypting:
gpg -d --batch --passphrase [PASSWORD] backup.tgz.gpg | tar -xzf -

The Backup Manager should be able to show the backups of all domains below the admin, including resellers.

According to https://support.plesk.com/hc/en-us/articles/360007305893 , it is required to enable resume uploads on FTP server side, however, it would be nice to have the option to disable resume uploading from Plesk side in case if there is no access to FTP server

Plesk does currently only support Amazon S3. Amazon Glacier is cheaper than S3 and also good for backups. Also support for Google Cloud would be great since at the moment, Plesk does only support Google Drive which is no professional backup (example: https://github.com/plesk/ext-cloud-backup-example).

When you want to Restore a Backup from FTP, first this backup it's downloaded to the Local Plesk Server and then the restoration starts.

At the end of the restoration process, the Local Backup it's still there, maybe it's better to save this space deleting this Local Backup and maintain only the FTP backup which was downloaded.

R1 Soft SBM is a stable and effective way of backing up the full server, and per user / per domain accounts. It is long overdue for support in PLESK, in the same way (and for the same reasons) that other major control panels already implement it.

Would love to see Rsync support added. SFTP is slow.

Backup task may increase server load. In order to balance it, it is required understand how long task has been running.
Currently it is possible to check only from log files, which is not very convenient. Please, add ability to simply check this info in Plesk UI.

Add an option to exclude domains / clients / resellers from a backup to the Plesk user interface.

Currently, it is possible only via command line:
http://docs.plesk.com/en-US/12.5/advanced-administration-guide-linux/backing-up-restoring-and-migrating-data/backing-up-data/specifying-data-for-backing-up.68839/

Include Mysql events in Plesk backups.

Currently backups created via Bacup manager or via
plesk db backup command, do not include mysql events.

Please, add a feature to be able to check Backup manager settings (including Scheduled backup settings), server-wide and for the particular domain via CLI. It would be very convenient for server administration to get information about backup settings in one place: for example, if there are multiple domains with different settings.

It would be nice to have backups uploaded to dropbox with a timestamp in the name, for example: dropboxbackup201911234

Plesk Migrator is a great tool but it don't migrate backup settings.
Please make this possible !

Have a better backup system (Can select exactly what files you want to backup in a good UI)

Since I installed the "Plesk mobile" extension, my daily server backup via Plesk (only configuration and e-mails) is much larger than before and gets larger every day! There is a log file called "MobileConnector.log" in that backup and this file currently is 150 MB in size (it increases by about 50 MB per month).

I would like to have an option to exclude this file. As it's part of an extension, this log file cannot be excluded via the checkbox "Exclude logfiles"! This option is not even visible, because I do not backup user files.

It's a nuisance having to go back to the main page to do a backup after uploading new or revised files.

Add the possibility to check the content of a backup so it can be reviewed and identify if the backup contains the needed files / information such as by date, name, etc.