As our interactions and machines are increasingly connecting and converging digital and physical worlds, how can we have a comprehensive design perspective?
Article Connecting design thinking with unified digital physical nature
In the attached article we discuss our approach of "Blended Interaction" which explains how users rely on and transfer their experiences from the physical world when understanding and using new digital technologies. Understanding this process of conceptual blending can help designers to inform the design of hybrid digital and physical experiences. Blended Interaction is based on theories from embodied cognition and cognitive linguistics and potentially could provide the approach that you are looking for.
Digital experience actually isn't too different from physical from an intellectual perspective...it's getting most people to understand that which is the difficult part.
The focus of Design Thinking is the human centred and the collaborative approach, independent if it is digial or physical. Its all about a positive emotional experience.
Maybe for you it can be interesting for you to read my paper about the digital media design process in museums. I proposed in this paper a model to re-think the process, grounded in 92 interviews with visitors, museum staff, designers and observations of around 500 visitors...I visualized the result of my analysis in a model that link the digital experience and the physical experience.
In the attached article we discuss our approach of "Blended Interaction" which explains how users rely on and transfer their experiences from the physical world when understanding and using new digital technologies. Understanding this process of conceptual blending can help designers to inform the design of hybrid digital and physical experiences. Blended Interaction is based on theories from embodied cognition and cognitive linguistics and potentially could provide the approach that you are looking for.
Although not personally involved in this specific question, I can recommend publications by our lab: Mixed Reality Laboratory, University of Nottingham. (please see here for general information: http://www.nottingham.ac.uk/research/groups/mixedrealitylab/index.aspx).
Especially, Steve Benford's work on trajectories (http://stevebenford.wordpress.com) might be of interest.
The point of "design thinking" is to overcome fragmented thinking and action and to integrate. The core idea is to align people (i.e., employees, customers, citizens, etc.) purpose (or vision), with resources (existing as well as newly generated/discovered) and structures (physical, informational, behavioral, etc.) in such a way as to improve human living. It is curious that we now find design thinking is being treated as a fragment in itself. As Katja observed, design thinking builds on human-centered design principles and methods that focuses on the human experience. So the answer to your question might well be: it is human experience that connects the physical and the digital. It is a human-centered design approach that helps you overcome such fragmented thinking and that leads to the integration of the physical and the digital. I strongly recommend a deeper engagement with design thinking and its meaning before applying it haphazardly.
Okay, while not focussed on design thinking, here's my take on your question...
The need to unify physical and digital assumes a division or distinction between the two already. This is basically a Cartesian dualistic approach. An Embodiment approach assumes that the body is the vehicle used by the mind to navigate a given environment, even when that environment is a digital/virtual one.
The question is very interesting and I think in a form or another as been troubling us designers of both products and spaces following the hip of computer interaction, aumengted reality, etc.
From the designer point-of-view the biggest limitation at the moment is that digital is mainly concern with pictures (moving, animation and tactile screens) and there is much to say on the others senses that cannot yet be resolved by the current technology at affordable prices (smells, sounds, tactile)
From the point of the view of the user the gain is very little at the moment since the possibility of interaction/customizing is very difficult in today's solutions.
From the legal point-of-view the only way to improve is if/when the user allows identification and the profiling. That might happen for alleged security reasons but will have a very difficult acceptation outsider special or professional environments.
So to summarise. That integration depends on screens, depends on customization and needs to expand for the interaction of the remaining senses since these are all necesssary to interact in the world. It needs to use affordable technology that can/may change the enviroments at your taste and needs and will affect the buildings of the future.
Some thoughts about this question in my presentation text for the Arts Track exhibition at the Seventh International Conference on Tangible, Embedded and Embodied Interaction (February 10-13, 2013. Barcelona) http://www.tei-conf.org/13/artstrack