Hello!
I was wondering if additional faces other than zlo are going to be implemented for the wall/piston fix in the next version of LAMMPS. I am interested in having more than one moving piston generating a shock in the same simulation box.
Unless you will do it yourself (and contribute the code to be integrated into the distribution), it is not likely to happen. I am not aware of anybody working on this fix. In fact, according to the git history, there have been no functionality updates to this fix for more than ten years; only maintenance updates and bugfixes.
Do you mean one piston for zlo and another for zhi? Is it possible to get the same effect with a moving wall of LJ particles?