Photobug56, do you seriously believe that LIRR is NOT going to have trains running in the reverse-peak direction on the third track? What the heck do you think they're building it for? Give us a break!
Actually, I think it will mainly be used for slow express service in the rush hour direction, so as not to make so much of a change in schedules that anti change riders will complain. And to be available if a train dies on either outer track. I've little to no expectation that they'll add any viable reverse commute service.
You're thinking logically. But this is LIRR, where logic seldom applies.