It would serve no purpose outside of causing flow degradation and turbulence.
An X-pipe or crossover pipe is put in to balance exhaust pulses between cylinder banks using individual exhaust pipes. (true duals)
When using a Y pipe there is no "true balancing" between cylinders. Matching pulses (not overlapping) is about the best you could hope to achieve. This would be accomplished by the Y-pipe pipe shape and pipe lengths.
Also spliting the single pipe at the outlets (quasi-dual) is just for looks. A properly sized single pipe would make the same power as a quasi-dual would...
