I want to try out Android TV and possibly develop an app for it. I want to see the OS first though. Is there a way to run Android TV in as a virtual machine, for instance with VirtualBox?
As mentioned in a comment to the OP, your best bet is to install the Android SDK and fetch the Android TV system images. Then, create an Android Virtual Device (AVD) with the TV image and run the emulator.
You won't have any of the apps that are preinstalled in, say, a Nexus Player, but you will get the idea around how this version of Android runs and what it is capable of.
[PRO TIP: if you're on OSX, using the x86 one results in HAXM acceleration enabled --> the emulator runs really smooth]