Okay. I don't see a use for number 1. Could you explain why it's important? It seems easier to me to just let each variable have its own type.
As for 2, I believe that's how MIT Scheme's (fluid-let ...) works. I suspect that if you give up property 1, then fluid-let would do the job you want.
Also, in the example you gave earlier (in your third email in this thread, beginning with "you need to combine fluids and dynamic wind ..."), I don't see the difference between set! and set~ semantics. It seems like the variables there have exactly the same semantics as fluids, except that you don't have to use (fluid-ref ...) to get their value.