I agree that there should be some attribute gains from hauling.
If a hauling skill is ever introduced, it could decrease the encumbrance from carried items, similarly to how Armour User decreases the encumbrance from worn items for the purpose of determining speed. The gains in hauling skill should be made pretty slow, because otherwise soldiers would train it up from carrying weapons and crafters would get it too from carrying ingredients. Even 1 xp / tile with very small chance of strength, endurance, toughness and agility gains, would be a bit excessive.
Skateboards don't fit the Dwarves, but I've seen Asians using Kick scooters to transport cardboard boxes with stuff over concrete and tarmac. I'm mostly fine with wheelbarrows, but would like the ability to assign per-dwarf or to everyone with hauling enabled, some sort of containers for hauled items, to avoid dwarves carrying around barrels of seeds, bins with items marked for reactions, hauling a heavy bin to pick up one item and other issues.
I find the "improved hauling system" to be pretty broken, so maybe we can brainstorm a good way to fix it. And no, setting 2 stockpiles next to each other, so that one takes from anywhere and has no bins and two takes from one and has bins is not a satisfactory "fix".