Christopher is, of course, free to white Trek however he wants (within the confines of canon) but I just don't see the need to try to "fix" elements of TOS. TOS is fine as it it. Writing a story that expands what we saw in an episode would add background and make the whole thing richer. Changing what the original author wrote, in this case Norman Spinrad, just seems counterproductive.
If you're going to change what has come before in order to make it more scientifically accurate (or plausible) then Trek as we know it will pretty much be undone. No FTL, no transporters, no human/alien hybrids, no psionics, no universal translator, no phasers. The list goes on.
I read and watch Trek for stories about humanity and how we can grow as an individual and a species. I'm not looking for a science lesson. Too much of Trek is simply absurd from a scientific perspective. And that's fine. It's not absurd in a Lost in Space/Red Dwarf/Hitchhikers Guide to the Galaxy sort of way. Trek is relatively believable within the confines of it's setting. There's eye rolling moments to be sure (The Counter-Clock Incident, One Little Ship, Threshold) but for the most part the "science" is believable enough that it doesn't take me out of the story.
We should be going forward, not looking to repair or fix or alter what's already been done. Leave the original authors work to stand or fall on it's own and let's move out into the great unknown.