Apparently soft environment specular does exist already and works in Kerkythea, which is free. Since this is software, I think it proves that the ability exists in software.

I don't even know how to use the program. I loaded an environment image. I did not add reflection to the material. It is a gray plastic with a specular effect enabled.

I rendered with ordinary ray-tracing, no radiosity or photo mapping or anything slick that Poser doesn't have.

Observe the specular effect of the entire environment sphere. Nicely convolved. This render took 8 seconds. I'm sure if I learned to adjust rendering quality I could make it look better.

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Renderosity forum reply notifications are wonky. If I read a follow-up in a thread, but I don't myself reply, then notifications no longer happen AT ALL on that thread. So if I seem to be ignoring a question, that's why. (Updated September 23, 2019)