Right now, if you want a Windows on ARM device, you have to buy a device powered by Qualcomm Snapdragon processor. Even though Surface Pro X is powered by a typical Snapdragon processor, it is running on a Microsoft-customized version of a Snapdragon chip. Basically, Windows on ARM is limited to one SoC vendor, Qualcomm.
Today, XDA-Developers reported that Qualcomm has an exclusive deal with Microsoft that prevents other SoC vendors including Samsung and MediaTek to deliver chips for Windows devices. The report also mentioned that this exclusive deal is going to expire soon. Once this deal gets expired, you can expect MediaTek and Samsung to join the Windows on ARM ecosystem. In 2023, you can expect Windows on ARM devices powered by different SoC vendors.