@Joe:
Indeed it is. These days, some people are willing to sacrifice battery life for a thinner laptop. But then again, the opposite speaks true for so many others.
A well-made 9-cell 100 Whr external battery is pretty compact, only weighing around 0.22 kg. And If they manufacture them using the same nano-tube tech as LG has accomplished with their Gram line of laptops, it potentially could be even lighter. This means that the Aero 15 with a 300 Wh battery (100 internal + 200 external) would come in at 2.6 kg at most. That's the same weight as my Lenovo Thinkpad P51, which I carry around every day with no problem at all. And since I'm a scrawny Asian guy who barely works out, I doubt a few extra grams would be noticeable for average folks.
The current market is perfectly capable of making this a reality, only the laptop ODMs are too apprehensive that the high costs associated won't pay off very well. What a waste of potential. Maybe in the future that will all change with a new electrode or something.