I would think a BT LE solution would serve most people well enough. With BT 5's increased range, the most likely situation is that someone misplaces them at home, car, or office, or even in their pants packet at the gym. It's enough to know they're in your immediate vicinity, or several feet away. There's probably a way to even have them emit a high pitched tone to locate them. The Tile app does this really well.
Likewise, to avoid leaving them behind in the first place, they could issue an out of range message to the phone (like the Apple Watch does), with a location and time stamp, so even if they miss the initial message, they will know where to go back and look. Tile even has a feature that allows the tracker to be located when in the presence of a Tile network node access, so potentially at a Starbucks for instance, or if someone found it where you lost it, and moved it somewhere else.
GPS would be nice, but likely impractical at this point. However, if there were room for the chip, power is not an issue. The same BT LE power would turn on the GPS chip only if needed. But this also drives up the cost of the AirPods, for something that's not likely necessary for most. If Apple finds themselves plagued by customers who continually misplace the individual buds out of the range of their iPhones, then they might fast track such an update. But I suspect this won't be an issue as to require such a dramatic measure. Most people are going to know if they're no longer listening to their music pretty quickly. In fact I'm hard pressed to come up with a scenario where someone might be without their case, and wearing something they can't easily slip them into a pocket. Setting them down in a gym locker while someone showers maybe, then forgetting them after getting dressed? But then, why take them off in the shower if they fit well enough to stay in through hair washing? ;-) I suppose a swimmer wearing a speedo at a swim meet and sets them down on the warmup bench, then wins and forgets he had them? Seriously, for those who have trouble with is sort of thing, they will need to get into the habit of putting them in a pocket when they take them out, rather than putting them down someplace. That will dramatically cut down on misplacing them, and the need for tracking them.
