I don't know the connection between the new commands "or" fluid dynamics,other than "new version of Minecraft." I mentioned carpet mod in the context of testing how much processing "stable" water (no new water blocks will be appearing) vs. dynamic water (a new source water block was just placed, where will it flow to?) What is the relative cost of each case on average, and how does the cost compare to an example of ten cows wandering in a pen?
There will likely be a difference, but I don't expect it to be much compared to a pen of cows or wandering mobs. I suspect the new fluid dynamics will add more, but not much more overhead since "fluid dynamics" are already present and must make choices for what blocks are barriers vs. blocks popped off as entities and passing through air. The bulk of the cost equation can be defined now with the carpet mod and a good set of test scenarios. I'm working 60 hrs this week. Next week doesn't look so good. The person setting up a good test and reporting won't be me.