if it uses ddr4? let's consider it had ddr4 2133. Same bandwith, worse latency . Slower console than with ddr3. But perhaps it has ddr4 running at a 50% higher clock ("ddr4 3200"). Is that a best case? The "slow" memory breaks the 100GB/s barrier! Latency probably is mediocre but you live with it. (the skimpy ~1.8GHz CPU cores that suffer low power ddr3 in hugh end tablets will survive that)
DDR4 has the same latency at as DDR3 at similar frequencies. Just check this article at Anand to get a better idea: http://www.anandtech.com/show/6619/crucial-demonstrates-ddr42133-modules
Or this one at DailyTech: http://www.dailytech.com/article.aspx?newsid=29633