It is possible to host several domains on a single project, and have different homepages for each domain.
This is a new feature thats available to projects created from 3 October 2017.
Virtual domains currently only works for user files - not to the app installed on the project.
How does it work?
To give each domain its own unique homepage, all you need to do is have a folder named as the full domain for each of your assigned domains.
So if you have a project with the following domains assigned:
Then you just need to create a folder with the domains files in a folder in the project root:
You can create these folders in your Dropbox project folder, or use FTP.
Note that the files are also accessible by using the domain as a folder name in the URL - ie
http://sub-a.domain1.com/sub-b.domain2.com/ will also show the homepage for domain2.