Sony's Xperia Z and Xperia X phone lineups have long lacked fingerprint functionality in the United States. Sony once explained this as a "business decision", leaving the term rather ambiguous. Some have speculated, however, that the software limitation is due to licensing issues of some sort in the States; indeed, almost all of the Sony Xperia devices that have made their way stateside actually do have the hardware for the fingerprint sensor on them. Since the fingerprint scanner being disabled is strictly on the software side of things, many users are able to circumvent the lockout and get the fingerprint sensor working through a number of methods.
For the most part, Xperia owners in the US found that enabling the sensor was as simple as flashing a different territory's firmware or a custom ROM on their devices. While special fixes were required in some cases, most of them ended up integrated into later custom ROM releases, such as with the Xperia Z5 Compact. With the upcoming Xperia XZ having a fingerprint sensor present, the speculation is that this one will meet the same fate as other Xperia models in the US and find its fingerprint sensor disabled on the software side when it hits the US.
While custom ROMs won't be available for a while depending on how popular the phone is with the development community, most modern Xperia models have shipped with bootloaders that can be easily or semi-easily unlocked. If this ends up being the case with the Xperia XZ as well, a US buyer could very well receive their new phone in the mail and flash the firmware for a different country's model the same day. Likewise, an unlockable bootloader means that custom ROM development is quite likely and will happen fairly quickly, if the phone happens to have one. Ultimately, how easy it is to enable the fingerprint sensor will be up to Sony when the device hits the States, but the fact remains that almost all signs at this point indicate that a fingerprint sensor will be present, but will also likely be disabled by default.