I believe this is a required capability. Most Web map frameworks allow you to use GeoJSON (at least) to create custom markers. I think we need to reduce the number of abstractions that are used to implement the functionality, however. By this I mean, for example in Leaflet, you have an object called a "Marker", which represents point locations using icon files. You can provide custom icons etc., however I believe that the "Marker" abstraction is one too many.
We need to support CSS / SVG styling of Simple Features geometries, if I might get to the point, but I guess that argument will be for another issue.
Anyway, instead of being undecided on whether this is a required capability, I think it should be marked as a green requirement.
I hadn't really been making any decisions about requirement status yet (other than in the initial sections I drafted as examples). But I agree, displaying marker points on a map is a basic requirement.
That said, we might want to separate out the "custom icon" bit into a separate capability. @nchan0154, did you consider that part when doing your capability review for this section?
@AmeliaBR I hadn't mentioned the custom icon part in my write up but I did take notes on whether or not custom icons were supported when conducting research, so breaking this out into a separate capability should be relatively quick and painless!