Hi,
You may know of all of these limitations already, but just wanted to list some things that I'm seeing.
The node layout is nice, but a scripting language would have been so much better, but assuming you're fixed on the nodes I'll tailor my feedback to that. I'm also not very familiar with Unity so some of this feedback might be my misunderstanding of what's available
A random node: Has 1 input, N outputs and randomly selects one of the outputs. Self explanatory, can be used for dialog variation, or controlling parts of flow
Local variables: It would be nice to be able to track and use variables in the event. Maybe we need to remember a response from earlier in a node that merged, or maybe it's needed to track a number or something different. I think integer support would be simplest and most powerful, you could use an int to represent state, a boolean, and you can increment and compare it.
With local variables: conditional nodes, we should have basic if statements comparing equality and greater than / less than, This should be to either other variables, or to fixed values
Global variables: a node that we can write and retrieve a key / value to a global place that persists across events.
Ability to set clothing: I notice you have a fixed list of outfits, but it would be nice if we could set the clothing to be specific by name, and the ability to purchase that clothing and add it to the wardrobe. Also the ability to query what clothing exists.
Adding priority to the events. We have a probability meter, but as you mentioned it competes with other events. It would be nice if there was also a priority where the highest priorities get evaluated first. That way we could ensure an event happens.
Ability to set game tags. Self explanatory I think, but this would let us provide alternative starts to some of the quest lines.
Being able to able call a different graph from inside a graph. I think you already have this actually. But This way we could use the graphs as functions. This would also be nice if this worked synchronously, meaning that we'll get a callback into our original graph when the graph we called completes.
Ability to schedule an event. We could use probability to control schedule events, but a fixed schedule that we can look at and evaluate would be nice. This way Zoe could elude to something in the evening and we can add a scheduled event for the next evening and have it guaranteed to work.
But it's a good start, but not having tools to control the flow with variables or if statements is very limiting.