It was a right move that VMware removed it and with version 4.0. This wasn't the case.
In place upgrade was possible and co-existence of version 2.x and 4.x can be achieved.
To list a few of the new features below:
Increase the number and speed of attachments through a new packaging and organizing the lifecycle of the Windows appsAble to manage Single Application or Group of Applications in a single stackEnable SSL encryption for SQL serverAppStack Migration Tool: use for migrating App Volumes 2.18 to App Volumes 4.0 Refer to this video for What's New in VMware App Volumes 4.0.
Mastering App Volumes Activity path here.