My only concern is the traffic durability. Roof coatimgs typically stay soft. If you cover it with sand, the sand may embed itself into the coating as you walk on it, eventually causing it to separate.
I tried Thompson water seal and was very disappointed. It is a parafin wax based sealer and not very durable for traffic on my deck. I much prefer a resin sealer like alkyd oil based stain/sealer.
The difference between the roof coatimg and Rhino Liner is that the liner is designed for serious abrasive and impact abuse, roofing is not. Granted, Rhino Liner is serious overkill but at least it's in the right class. Linoleum would be a good choice because it is cheap and replaceable and fairly durable. Personally i prefer concrete for outbuildimg floors for all the reasons you mentioned. You can't hurt it and bugs cant infest it
There is always ceramic tile.....
I had the same concerns about the roof coating but this particular one dries firm. The dried film is not sticky but not hard like bed liner either. In our coop floor application it will be always be covered with several inches of wood shavings as we are doing the deep bedding method so no issue with traffic durability. Deb's application is different so I'm not sure if it would be the best choice or not as it would have foot traffic in that application.