Here's one of the main Elliott founded reasons that lead me to think the 4th will require another low to complete.
The corrective channel was originally set from the top, plus the next 2 significant pivots (highlighted by the red arrows), which provide the slope and range of the correction. The blue channel is a clone of that, and seems to capture the angle of the progressively deepening lows, leading to the intersection with the lower parallel of the yellow base channel.
This doesn't mean it has to happen like this - it's simply an apparent possibility according to the EW theory. But they do seem to have a habit of finding these geometric points before continuing the larger degree trends.