[palmer]

My theory is that any N theories can be "unified" by postulating a new universal theory with N + 1 dimensions.

[The_Reader_David]

Actually you're very close to the latest two iterations of string theory: "M-theory" (M could stand for matrix, the next to last iteration, or membrane). The string theorists argue that because four or five of their attempts approximate each other in certain limits, they must be aspects of a single as yet undiscovered theory. (The limiting arguments are non-rigorous, not usually a consideration in physics if experiments can be appealed to, but they can't in this case, and the overarching argument is completely bogus: quantum mechanics approximates classical mechanics in a certain kind of limit, and this is not evidence of a missing theory which both approximate which is the 'real theory'>)