The update is a small one but handy nonetheless. In fact, the only thing new that's listed in the official software change log is support for cloud printing through Wi-Fi, Bluetooth, Google Cloud Print, and HP ePrinters. Other enhancements included within the patch, such as battery life improvement and a Microsoft Exchange e-mail fix, are essentially band-aid measures.
It's worth noting that T-Mobile technically doesn't offer its own version of the Moto X handset. Indeed, the carrier pushes customers directly to Motorola to purchase the company's unlocked GSM model. Because of this, I'll bet this particular model will be first concerning future updates as well. As for the other carrier branded models of the Moto X and their respective 4.4.2 update, Motorola lists them as "coming soon."
If you're using an unlocked Moto X and want to check for the update manually, open the Android settings menu and navigate to Settings>About phone>System updates.