I think an interval that fluctuates randomly within a certain range of a target power would be useful as this better simulates real-world riding (especially on rolling terrain) than fixed or ramping intervals.
The ability to absorb fluctuations while riding at a given average power is something you need to develop, in my opinion.
Another idea would be to obfuscate the length or exact intensity of an interval in order to develop your ability to deal with “open ended” situations, something that is a big part of racing. E.g. “??? minutes at 275 watts” or “5 minutes at ??? watts” I often find that knowing exactly how long and hard an interval on the trainer will be becomes somewhat of a crutch.