The expected requirements are those required for Ark: Survival Evolved. There is a statement about the computers that SBS is using for development somewhere around here.
For clients, performance is expected to be driven by the requirements of the Unreal 4 engine (UE4). There could be surprises, such as local data requirements exceeding the 16GB that SBS development computers currently have installed.
Since the computers that SBS uses are more powerful than mine, I am anticipating the need to upgrade to at least one new computer about the time Exposition rolls around. I probably won't do so before that, at least just for CoE, because I don't expect to know what the recommended specs are until then.