Yes, you could have different possible production rules for a given symbol and sample from them according to some distribution. You could also just randomly per

Yes, you could have different possible production rules for a given symbol and sample from them according to some distribution. You could also just randomly perturb/fuzz a given iteration of the system. A deterministic system is nice, however, because you can make changes to the production rules and rendering without having to worry about as many possible outcomes (introducing stochastic production rules increases the number of possible outputs combinatorically). This is not too much of a problem if you're just making cool fractals for fun, but if you're doing procedural generation with L-systems then you have to keep an eye out for degenerate cases. For example, if you're generating foliage this way, you might get plants that grow into the ground or in weird non-biological patterns.