There are 16 Allomantic metals, however, there were commonly believed to be only eight. In Stormlight Archives, we are given ten surges, ten essences, ten orders of Knight Radiant, and so on. Are we seeing something like on Skadrial, or is Sanderson drawing our attention with a new 'Law of Ten'? The 16 rule references the 16 Shards of Adonalsium. Would the new law of ten be referencing that there are only ten shards left after Odium killed five and Preservation and Ruin formed Harmony?