Actually with this release threadripper 2 will support DDR4-2933 which should increase the memory bandwith and the throughput of the infinity fabric if I'm not mistaken (I am pretty sure infinity fabric runs at the ram speed)
I've seen some people hit 3466MT/s on higher-end more expensive RAM on AMD's 12nm stuffs (Ryzen 2). So that's probably the practical limit.
3200 MT/s on Hynix dies is probably a reasonable expectation.