[holmburgers]

...but doesn't seem to have many practitioners in the alt photo world - there must be a reason...

I wouldn't be so certain, yet. Just because no one uses CMC gum as a substrate is not necessarily because it won't work, but because hardly anyone does original experimentation. You know of it because you're a potter, but I'd bet that most alt processors don't know what it is (I certainly didn't before PE mentioned it to me privately).

The only way to be sure is to try it yourself and evaluate the results.

I'd encourage further exploration.