The update from Zen to Zen+ on AM4 was around 13-15% - Zen(14nm) to Zen+(12 nm) meaning IPC (3-5%) + frequency boost CPU (7-8%) + DDR4 frequency boost (2-3%) - not only IPC.

What we will get with Zen2:

a) more cores for AM4?
b) increased frquency and IPC?
c) a chiplets architecture similar to Epyc - Rome also for AM4 platform?
d) a combination of the above stipulated possibilities?

Anyway the lack of scaling for the threadripper 2970WX and 2990WX due to the 2 compute units without direct access to RAM will be history on 7nm, with the new chiplets architecture on TR4.