Double capacity would add about 60 pounds.
I was wondering about his so thanks for chiming in. I think the extra weight would not be an issue for some riders depending on the type of riding they are doing, for example street, or forest roads.
Personally, I would not want an additional 60 lbs on my 260-270 lb trail bike (not sure what the Alta weighs), but that is just my perference.
If I had to pick between a bigger battery pack that offers 50% more range at an additional 60 lbs, or quick change battery capability for the original spec batteries I would go with a quick change battery.
And of course, having both would be another option. Stock spec battery for single track type riding, larger capacity/size pack for road, forest roads, etc.
Additional battery pack options are a good thing! (And...the stating the obvious award goes to...Lol)