Virtual NAS solutions do fit into an SMB NAS environment, as long as you can find the benefit of consolidating various SAN islands into a single solution. In a typical SMB environment, there is a potential to have data strewn all over the place in the form of ad hoc file-serving environments. User data can stay resident on employee desktop and laptops, exposing it to the risk of getting lost or exposing it to unauthorized individuals.
So by consolidating it in the form of virtualization, it allows your company to get rid of such SAN islands and ad hoc file-serving environments and, more importantly, enforce a common policy for security, data protection and access.
NAS virtualization is one of the ways you can bring about this consolation. The other option to consolidating NAS is to invest in a scalable environment and then migrate everything to this new environment.
Virtualization has been around for awhile. It hasn't gained or lost any popularity per se. Most vendors are now offering virtualization as a function in their products, so it's something that you don't have to buy extra to install it.