I think the question being really asked here is would it be worthwhile/practical to add enough of the ammonium based chemical to fully react with the Hypo? Whold that even work or do the old formulas represent the most that can be expected to react....
ammonium thiosulphate is normally supplied as a liquid with a relatively short shelf life. a powder that was stable which has the fixing power of a Liquid fixer concentrate might be a useful formala to have on hand. I know I can get the Ilford rapid fixer with a slight delay at a local store. I don't dare mail order liquid fixer in the winter.
An all powder fixer would not have that worry. The cost factor may be overshadowed by the convenience factor.
I also wonder if the Amaunium Thiosufate is also used as a water treatment chemical? which would assure it being available on the market.