I think that an advanced feature that could possibly be created is to have the action of a rule be able to add/delete/modify another rule or rules. This allows TWINE to alter its own behaviour depending on what happens to it. A sort of configurable finite state machine. Each rule would need to be identifiable and access to the trigger and action allowed. This means that a sensor reading can cause different things to happen at different times even though the value of the sensor is the same.
You could even have an array of TWINEs and allow them to alter each other's rules (ala twineID:ruleID:trigger|action). This is obviously for advanced users but I'm sure there is someone out there who would be able to tease some interesting emergent behaviours out of such a network which would be cool to see. I can see a room full of TWINEs with all their LEDs forming some weird pattern like Conway's game of life animations.
Practical uses would, of course, follow later.