The second iOS 12 beta has gone beyond just spotting the AirPort Express in the Home app, adding more weight to speculation that the discontinued device will be an AirPlay 2 target in the future.
was able to verify the appearance of the 2012 redesign of the AirPort Express in the Home app in the first iOS 12 beta. However, when tapped, the device was not added as a HomeKit peripheral -- but visibly failed unlike the first time around.
After the second beta, the Home app pops up an alert that an AirPort Express update is available and needs to be applied. However, no update is available, and the app fails in the same manner as the first iOS 12 beta Home app did.
The last update to the AirPort express was in December 2017, for the KRACK exploits from earlier in the year. AirPlay 2 wasn't in testing at the time, with the AirPort patch happening well after the first round of testing of the technology, and before the abortive second round with the iOS 11.3 betas prior to its removal very near the end of the cycle. The update prior to the KRACK fix to the AirPort Express was delivered in December 2016.
This is now the third time that the AirPort Express has appeared as a HomeKit accessory and potential future AirPlay 2 target, and done nothing when selected. It was pulled about two weeks after the first iOS 11.4 beta.
Since that first appearance, Apple has killed off the AirPort line in its entirety.
The refinement of the process in iOS 12 is the best sign so far that the peripheral will be added as an AirPlay 2 compatible bridge for wired speakers. However, support is far from guaranteed and may still be stripped out or repurposed for an as-yet unknown future device from the company.
Once again, other AirPlay-compatible devices were tested after the re-appearance, with none appearing in the Home application.