I think Sasuke will never use Hashirama's arm. Kishimoto deliberately drew him wearing a cloak that covers his missing arm in 700. And that's what Sasuke will be wearing from now on. But it's hot in the summer. A hand cut in half doesn't really look nice on the beach. Supposing, he learned to cast jutsu with one arm like Deidara, could he create an arm and keep the jutsu activated for some time like Tsunade does?