The only undisputed champion of interaction models/devices since the mouse is the touchscreen. No contest. The trend and industry is trying, often too hard, to push the next frontier of interacting with devices toward voice. While I think voice interaction is crucial, I don't think it is being thought of in the right way yet.
There are inherent problems with voice. Natural language recognition isn't perfect, and likely won't be for a while. If the system has "keywords" you've failed before you shipped and the biggest concern of all is probably privacy. I'm not talking about Google or government knowing your every move type of privacy, I'm talking about old fashioned privacy. "Don't let the guy next to me know what I'm saying to my wife" privacy. There is a reason messaging is still king (cough, WhatsApp for $19 billion). Messaging is, and will be for the foreseeable future, a major player in how we communicate. Yes people will dictate messages, but often we're in public or a quiet place and just don't want to share what we're saying with everyone. Expect a piece on this soon, but let's leave it there for now.
So how do we advance to the next interaction model if it isn't voice? There is nothing left between us and our content; we are literally touching it. No more mouse or scroll wheel in the middle. To answer the question, you've got to change the perspective a little bit.
I think the next interaction model is going to be proactive and intelligent technology. We have seen signs of it today, Google Now being the best example by far, but don't forget Android's (third party) context aware lock screens. These are just the start, but it is a sample. Your first thought is probably "that isn't an interaction model, I still touch the screen or use voice commands." That is true, for now. That changed perspective I was referring to is to accept that voice and touch are likely to be around for a very long time. They'll be a big part of this. This proactive technology isn't replacing touchscreens any time soon, but it will fundamentally change how we use technology. For the first time, the interaction will be a two way street. That is the interaction model breakthrough.
There are concerns and problems to be solved. We've gotten used to getting this type of thing for "free," but nothing is really free. If you aren't paying for the service, then you are the thing being sold. To achieve this level of proactive technology, the devices will have to know us very intimately. This means collecting data, a lot of data. For now that means privacy is diminished, but eventually that will (largely) come to pass. Encrypted devices send encrypted anonymous data to servers to process and analyze with anonymous (encrypted) results sent back. As with anything with technology, this can and will be hacked, but if the value is high enough people will allow it. They've moved all of their communication to free email and free (or free-ish) messaging haven't they?
It is tough to say what the solution will look like, but I anxiously await the day my technology drives the interaction with me and not always the other way around.