I wouldn’t discourage a heap, I think some programs do well to using something like that if they need to. What I normally use don’t need it, so I never had to mess with it. The more canon usage of memory with uxn, to me, would be something like Porporo which gives each uxn instance some memory to do their little tasks, and then takes it back.
I like to think of a computing system that would make use of hundreds of uxn instances where each have limited memory to do a task, like cells in a larger organism, each uxn cannot interfere with the memory of the others, like a bit of protected state.