According to a new report, Xiaomi's upcoming flagship will sport an in-display fingerprint scanner, though we're not necessarily looking at the Mi 7 here. This info comes from XDA Developers and FunkyHuawei, and is based on leaked firmware files. The source found two separate firmware files for the Mi 7, in the first one the device is codenamed 'dipper', while the name of the second one is 'dipperold'.
Now, based on the name itself, it's easy to deduct that the dipperOLD is a scrapped firmware for the Mi 7, and the main difference between these two firmware files lies in the fingerprint scanner. The dipper firmware files suggest that a fingerprint scanner is sourced from FPC and Goodix, which is quite usual when it comes to Xiaomi's smartphones, but things are a bit different in the dipperold firmware, as Synaptics and Goodix are mentioned there, and Goodix's sensor comes with a different name there. In the dipperold firmware, Goodix's sensor is called 'goodix_fod', and the 'fod' probably stands for 'fingerprint on display'. The 'MiuiKeyguard' app, which is responsible for the lock screen, also suggests that an in-display fingerprint scanner may be coming, and several other hints were found in the firmware.
Based on what was mentioned here, it seems like Xiaomi considered using an in-display fingerprint scanner in the Xiaomi Mi 7, but gave up somewhere along the way, as that firmware file is now named 'dipperold', and there's no reference to the in-display fingerprint scanner in the new firmware (dipper). So, either Xiaomi decided to scrap its plans for the inclusion of an in-display fingerprint scanner altogether, or the company is planning to include it in a different phone, not the Xiaomi Mi 7. Both options are quite possible at this point, but it seems like the Mi 7 will not sport an in-display fingerprint scanner, at least not based on the provided info. The Xiaomi Mi 7 is expected to become Xiaomi's second flagship in 2018, following the Mi MIX 2S which was announced yesterday, and even though we don't know when exactly will the Mi 7 land, chances are it will arrive in the summer.