[DrJJWMac]

The terminology Defer fits especially to what you do to a task when you push it away to be handled later. Tasks without Defer (until) dates are essentially always waiting for your immediate attention. The implication when choosing a Defer date is that doing so implies a reason outside of my control. The danger with choosing a Start date is that doing so could be interpreted to mean that I have a perfectly free choice to pick that date of my own volition.

IOW, Defer means ...

Keep this task entirely out of my attention span until a specific time defined (exclusively) by when external factors that are currently beyond my control and are blocking it from even being possible to move forward will/should disappear.

... whew!

I can see Defer (until) becoming the de-facto for Start (on).

As a tangent to this, what I could not accept would be a push now to eliminate Due dates in OF as per the strict GTD guidelines. The "due dates are strictly for calendar items" paradigm worked for the days when GTD was handled with a hard copy binder where both the calendar and the planner were integrated. That paradigm does not work today where we have electronic binders with a calendar app separate from a planner app (sometimes by multiple clicks).