ETS (Equivalent Time Sampling) resolution is only limited by the ability to time the samples, given a repetitive signal. I think earlier Rigols even had it, but they've dropped it as a feature, which I'm guessing is because of how the trigger is implemented now.
Low end DSO manufacturers dropped ETS when digital triggering became less expensive than analog triggering. Digital triggering is less expensive now because increases in integration made digital logic less expensive. Analog triggering does not benefit from increases in integration.
What does analog triggering require than digital triggering does not?
1. Trigger pickoffs for each channel.
2. Analog multiplexing to select the trigger channel.
3. Analog multiplexing to select the trigger coupling.
4. A fast analog comparator.
5. An optional time delay counter to measure the difference between the sampling clock and trigger.
In comparison, digital triggering might as well be free with increases integration.