I'm yet another seller (albeit with 21 years experience), who has no desire or need to use 'The Simple Delivery' scheme -- and foresee it just adding an unnecessary layer of complication for eBay admin itself. You might say, 'fair enough, it's their headache', but I suspect the increased admin man-hour costs will be passed on to Buyers and Sellers alike.
But my understanding (from a long conversation with an eBay agent last month), is that sales that are under 100g in weight and no more than 'Large Envelope size' _can_ still opt out from 'Simple Delivery'. Perhaps this is some silver-lining? And if no one except the seller and buyer are involved in _the objective truth_ about how much something weighs, and its size ...it's almost as if certain liberties can be taken in our listings, to retain our own freedom and pricing?