Unification of theory has nothing to do with if exist speed limit or not. Unification of theories is possible if each theory can be derived from a bigger theory. If the theories deals with elements that are independent and has nothing to do one with each other, unification never will be possible.

The Einstein's Theory of Relativity is very funny. Einstein took Lorentz Electromagnetic theory, a wave theory. Took from Thomson electron's theory the famous E = mc2, waves and electromagnetism again and then put gravity that was not existent in any theory and then ignored all waves, electromagntism, and electrons remaining only gravity and the imposed speed light limit, limit that doesn't exist in any of these theories.

Stupidity also evolves!