| Verocras |
Assuming that the "when" in the description of Swarm Strike means "at the same time as" and not "while", I would re-write the Swarm Strike description as follows, to try to more precisely describe it. This isn't meant as a change, just as a description of the current rule:
At the same time as you form your sheath array, you can use a nanite surge to gain Swarm Strike as a special unarmed melee attack. The attack deals lethal damage, lacks the archaic trait, and has an item level equal to your nanocyte level. You can use your Constitution modifier in place of your Strength modifier for attack and damage rolls for this attack. While the Swarm Strike is active, you threaten squares within your reach. Using a Swarm Strike requires you to have at least one hand free (unless you have the Improved Unarmed Strike feat).
For each attack, you can deal bludgeoning damage, piercing damage, slashing damage, or any two of these damage types. At 3rd level, you gain a unique weapon specialization with your swarm strike, adding 1½ × your nanocyte level to its damage rolls (instead of just adding your character level). At 7th level, this unarmed strike gains the thrown (20 feet) special property, and while you have at least two hands free, your weapon specialization damage bonus with this weapon increases to 2 × your level. At 11th level, while you have at least two hands free, your swarm strike gains the reach special property. At 15th level, the range increment of your thrown swarm strike increases to 40 feet, and it increases to 60 feet at 19th level.
You can use this ability only while your sheath array is active. So long as it remains active you do not need to use an additional nanite surge to make each attack.