Knowing Apple, they would just go for the 'even lighter' approach, and insert a battery half the size of the current-ones... A battery lifetime of 8 or 12 hour

Knowing Apple, they would just go for the 'even lighter' approach, and insert a battery half the size of the current-ones... A battery lifetime of 8 or 12 hours is plenty, and going beyond that isn't that much of a marketable strategy, unless it has to become 24h+ or something. A lower weight approach however would also mean a lower BOM for Apple, and more profit, while being able to shout "1/3rd lighter!" - and that's an easy sell :)