Chinese mobile phone company Vivo already have a fingerprint scanner which works under glass or even metal.
And there rumours the Samsung Note 8 will include an under display sensor, which will be announced before the iPhone. So we will wait and see.
The Note 8 has already leaked in full, it has the fingerprint on the back, just like the S8. And whether Vivo have come up with something that works under the display is not really relevant here. The iPhone is going to be produced and sold in the hundred of millions devices, I highly doubt that the Vivo's tech is available in the required quantities and we don't even have a clue about how good it works etc.. And whether they would charge ridiculous fees in order for Apple to license the technology.