As, always, PE, thanks for your ongoing contributions...
From an academic standpoint, a more effective preservative is interesting. But given reasonable care in drying and storing hand-made tissues, they do not seem to be particularly susceptible to picking up nasties, and the broader experience base seems to suggest that Thymol is sufficient. In all my reading of various carbon threads and fora, I don't recall seeing any mention of Thymol-preserved tissues deteriorating due to microbial or fungal action.
Speaking from my opinion, here, if that advanced preservative is useful or necessary to your emulsion work, that should be the primary focus (and "market"). If it is readily obtainable, then some may choose to use it for their carbon tissues or other purposes, but I doubt it would be the driving force in continuing development of it. I hope that doesn't come across as too discouraging, but that's the way I see it.