I found Fishkin’s conceptualization and analysis of TUIs along the two dimensions of embodiment and metaphor to be useful frameworks to think about various TUI. However, I also felt that there were some fuzzy/grey areas wherein it wasn’t clear if a TUI is one or the other or overlaps/spreads across categories. I found the taxonomy to be interesting tool for analysis and organizing but not as useful for innovation.
The example that came to my mind was that of virtual reality. It’s hard to perfectly fit the interaction in the virtual world along the dimension of embodiment wherein the output to the user’s action is happening in the virtual world. Also, along the Metaphor dimension, I felt like VR technology doesn’t fit perfectly in any category (except for none). Similarly, as innovation makes way for new technology, these boundaries of fuzziness could increase.
So, while Fishkin’s taxonomy is a very useful tool for analysing and conceptualizing, I would consider keeping it in my toolset for that purpose and use it within the larger context of user needs and user interactions to help define the solution space of the particular problem that I am working on.