I'd like to discuss the atrocity that is the drop chance of this item.
This is the situation: The motif chapters and very rarely the whole book have a chance to be found in Treasure Chests around Vvardenfell and The Halls of Fabrication. This is the only way to generate this item. As anyone who has tried looking for this motif knows, it's practically impossible to find. Treasure Chests, if they spawn, are generally well hidden. You basically have to scour every corner and compartment of a set area to find them. It is even harder to find an Advanced difficulty or even Master difficulty chest. On the rare occasion that you do find a Master Chest, the chest with the best possible drop chance modifiers, it's not even a guaranteed drop. I've heard reports of other players that try to farm this motif and don't get even a single chapter after opening hundreds of chest including 10+ Master Chests. I can't speak to how close to the average these numbers are but this is a pretty common outcome as far as I can tell. It is not surprising that the TTC suggested price for these chapters is generally between 40k and 60k with the Chest-pieces between 100k and 120k.
Now, lets compare this to another Motif that holds the same role within its Chapter expansion. The Psijic Motif from Summerset. This Motif's Chapters also drops from Treasure Chests and yet they sell for less than a tenth of the Bouyant Armiger Motif. There appear to be 2 reasons for that:
1. The drop chance from Treasure Chests is significantly higher
2. It drops from other sources too!
That's right, it also drops from Abyssal Geysers and Pools, Delve Bosses and World Bosses.
These 2 motifs fulfill the same role. They are Overworld rewards for the Morrowind and Summerset Chapters respectively. In my opinion that sets them equal in function and value. There is room for a difference in value due to different challenges one would have to overcome to obtain either but I really don't understand how ZOS could possible justify such a large difference in overall drop chance between these 2 Motifs!
I believe that the Buoyant Armiger Motif should be that abundant as well! It could perhaps be tied to more challenging content than the Psijic motif since there is no way to improve the drop chances through skill line progression for this motif. By my estimation, the drop chance of Buoyant Armiger Chapters from high-level content (such as World bosses and perhaps Master Chests) should be similar to the drop chances of Psijic Chapters from mid-level content (Abyssal Geysers and Delve Bosses) at maxed out skill line progression.That is assuming that the drop chances of both Motifs improve with the difficulty/rarity of the source. Now, Vvardenfell doesn't have Dolmens of any kind and no mini invasion events throughout it's map. That rules them out as a possible source for this Motif. To stay consistent with that missing activity, I think it wouldn't necessarily have to drop from Delves either since they are very similar in difficulty level. However, it absolutely should drop from World Bosses. They are challenging and warrant an appropriate reward like this Motif.