plaster shower walls, how to do them today?
What you cover the walls with certainly does matter if it can be damaged by water, as many forms of plaster can--such as modern gypsum plaster, which softens and disintegrates in the presence of water. The only way I can imagine a plaster shower working is if you perfectly waterproof the cementboard with a paintable waterproofing membrane like RedGard (preferred) or poly sheeting behind the cementoard, and then use old-fashioned lime plaster, and then paint the lime plaster with multiple coats of a waterproof but vapor-permeable silicate mineral paint or some other type of vapor-permeable waterproofing agent.

But this is a totally non-expert perspective; I have never built a plaster shower and the whole idea sounds risky and ill-advised to me. If you want to go with this approach, you should probably bring in a pro.