Backup restoration - all databases of a subscription affected
Would be a good UX/UI improvement to get informed that ALL databases of all domains under the subscription would be restored in case the subscription restored from the backup. (all configuration and content)
From the comments we understand that it is desired to restore only specific database(s) when doing a restore. That option is already available. Instead of restoring "all content" you can select "databases" and then pick the databases that you want to restore. As a database is not physically linked to one website project, it is technically not possible to auto-select the right database that a website project uses to auto-restore along with a website restore.
Let's clarify the problem.
When you have-
If you choose to restore site: sub1.domain.com, its logically clear to you that you want to restore the DATABASE of this subdomain only and not touch and other databases.
This suggestion should be updated to: ALLOW TO RESTORE RELATED DATABASES TO SUBDOMAIN instead of all databases of the whole subscription when you choose to restore only one subdomain: sub1.domain.com