Yes I do refer to casein/DAS as a gum/dichromate replacement. Casein printing has a lot in common with gum. With DAS, printing is very straight forward. Developing a DAS/CAS print is ultra fast! My gum negatives are too flat for DAS/casein but that might be corrected by cutting down the casein/DAS ratio. Now I am using a 8% (powdered) casein solution, with 2% ammonium carbonate and 1 gram DAS (1%) per 100ml. This is a higher collo´d/ DAS ratio than I am using in carbon printing. I will test if I can cut that in half and see what that does with the tonal range.
A spray gun might work. It would be interesting to have such a coating option, because brush coating casein is somewhat more difficult than gum. And for both techniques, coating large surfaces is not evident. But be careful, any toxicity of DAS has never been discribed, but this might be due to the fact that there has not been much research in this respect. But with the knowledge we have it would be much much safer than spraying dichromates.