The virtualization of the settop box brings great rewards for operators: that is what the message of Ziggo is. Similar to cloud computing: by moving more functionality onto servers and having less in the clients it becomes much easier to upgrade and improve.
Ziggo is using a cloud based interactive TV UI in collaboreation with CI+1.3 modules (running a very basic interactive TV shell) and basic STBs to deliver interactive services to all of its customers. Without any upgrade of the STBs. That seems like pretty good value.
The interaction speed (and superduper animated graphics) are the achilles heel of the system: standard delay on a key press is more than 0.5 seonds which is quite long. But this is a specific property of the technology selected by Ziggo; other forms of virtualized STBs can do better than this. But the PayTV world is too divided to try to create a standard solution; they could possibly get their act together; maybe use the RDK initiative and channel part of the energy there in this direction (unfortunately this may create too much of an existential tension).