It sounds like a back to square 1 case. If running tails in VM you will have 2 systems to secure instead of 1 (the host and tails) which means more attack surface.
What are the advantages of this? How do you secure the host in such case (assuming tails is all safe in such use)?
I don't think their are advantages in running Tails inside a VM from a security point of view. But there are drawbacks. Nonetheless, it has some advantages on a usability point of view. For example, we use it a lot for testing.
Other distros take advantage of virtual machines from a security point of view. See Whonix. But that's a different project.
Tails and Whonix are different projects that we see as complementary since they try to solve different use cases. Tails is a live system, you can use it anywhere, it's amnesic and leaves no trace. Whonix is a general purpose operating system, that enforces Tor, and prevents leaks.
So they are different because they answer to different questions. But we support this project, and are in good terms with the main person developing Whonix, who is participating on our mailing list.
For more info, have a look at the comparison between Whonix, Tails, and Tor Browser Bundle on the Whonix website.