Infos available are still hazy about the next generation of Russian main guns, but it looks more and more likely that the 152mm option would be retained rather than the 135mm, should anything new be actually considered. According to rare sources (
here is the only free-access article I could find, see if you can translate it) the future Chinese tanks is also supposed to use a 152mm smoothbore gun in the first stages.
Problem is, where is one supposed to find data about that 152mm gun which, as far as can be known, hasn't left the drawing board?