The HTC 10 for Europe is said to be updated to Nougat soon with the date of availability rumored to begin within a few week's time. Although a few weeks is not too far from now and that means the update should start rolling out to users who own the HTC 10 in Europe around the middle of February, the update is also geared only towards devices in Europe, including carrier devices alongside the unlocked model. The Android 7.0 Nougat update had already started rolling out to various other models of the HTC 10 prior to now, with the T-Mobile model of the device beginning to get the update as of January 5th.
Although the update to Android 7.0 had already began for some, HTC reportedly stopped the update to the latest software version due to there being bugs that had to be smoothed out before sending it out to more users, which is why some models of the HTC 10 in other regions have yet to receive the upgrade. Although no other regions are mentioned, it's entirely possible that HTC is working on the software for the HTC 10 for other markets, although when the update is pushed out to more carrier versions of the phone in the U.S. all depends on the carriers, and even if HTC continues the software update for more unlocked U.S. models of the phone around the same time as the European model, there's no guarantee that the carriers will push the software update out at the same time.
Beyond U.S. carrier models of the HTC 10, such as the one from T-Mobile, the U.S. unlocked model of the phone began getting the update to Android 7.0 Nougat as of last November, so some users have had the new software for a while, which also showcases that HTC was quick to push the new software to their 2016 flagship device rather quickly as that was right around the time that Google officially announced and released Android 7.0 Nougat. For users that are among the group that don't have Android 7.0 just yet, the update may not be far off, and it's always possible to check for the update manually from the settings menu.