In real life we use visual cues to stay in the draft. It’s easy to judge the distance between your front wheel and the rear wheel of the rider in front. If the gap is too big or growing, add power. If the gap is too small or shrinking, ease off a bit.
It’s not so easy to judge that gap in Zwift. Mostly I’m using views where I’m looking from behind my avatar and can’t even see my front wheel.
Maybe what’s needed is a Distance or Gap Bar: A thin vertical bar on one side of the screen representing the distance to the rider in front. Distance from 2 m down to zero. You could adjust your power to stay in the draft based on the gap and how fast it’s growing or shrinking - just like IRL.
This would be most useful when trying to draft off a single rider, or a small group. In a large group, a Distance Bar shouldn’t be necessary.
In either case, it would still be nice to see how much drafting benefit we are getting - a display of watts saved or a percentage of power vs. what we’d have to put out to maintain the current speed in the absence of any draft.