There's been a lot of hype lately around on-screen or sub-screen sensors, most of which are designed to remove bezels or even notches from the display. The first was the fingerprint scanner, now followed by the front-facing camera. Apple has long since abandoned the former, preferring to leave a wide cutout for the Face ID functionality that replaces the fingerprint sensors. However, while the company hasn't abandoned Touch ID entirely, its next version may not appear on the iPhone 13 later this year.
When Apple removed Touch ID from the front of its phones, it didn't follow Android's tradition of moving the fingerprint sensor to the back or side. Apple also didn't follow the trend of using on-screen fingerprint scanners, and instead stuck with Face ID. Apparently, this is not the company's ultimate goal, but an in-screen Touch ID is still a long way off.
According to Bloomberg's Mark Gurman, Apple has been testing a screen version of Touch ID for some time now. While it's intended for a future iPhone model, it likely won't appear this year. Moreover, sources in the supply chain say that there is no timeline for the introduction of this technology yet.
However, the scenarios for implementing Touch ID in the screen are quite curious. One option is that iPhone Pro models will use on-screen Face ID, while base models will switch to on-screen Touch ID. The other option is that non-Pro models will continue to use notches, while the premium lineup will use Face ID under the display.
Both scenarios, of course, require Apple to implement on-screen Face ID in addition to on-screen Touch ID. Clearly, the first option is quite difficult to implement, and Apple is unlikely to launch a solution that it's not happy with in terms of quality.