A unification of all martial arts would either be (a) all martial arts in their entirety or (b) a new martial art consisting of fragments of all previous martial arts.
In the case of the former, each individual martial art would retain its distinctive theory and methods, and no unification in any pragmatic sense has actually occurred. In the case of the latter, yet another martial art with its own distinctive theory and methods has been created.
G.K. Chesterton wrote:
Anarchism adjures us to be bold creative artists, and care for no laws or limits. But it is impossible to be an artist and not care for laws or limits. Art is limitation; the essence of every picture is the frame. If you draw a giraffe, you must draw him with a long neck. If, in your bold creative way, you hold yourself free to draw a giraffe with a short neck, you will really find that you are not free to draw a giraffe.