AirPort Express is popping up for users trying to add a home kit accessory in the iOS 11.4 beta, but the appearance is not universal, nor does the networking peripheral actually get added when selected.
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 the technology, and before the abortive second round with iOS 11.3 betas prior to its removal very near end of the cycle.
The appearance of the device in the iOS 11.4 beta is the first time that it has appeared as a possible accessory.
The development status of AirPort hardware is somewhat up in the air,saying that the network hardware development division has been mostly dissolved, with some engineers relocated to the other departments and others keeping the device as safe as possible, for as long as possible in software.
The appearance of the old hardware appears to be nothing more than an aberration of the testing process, but the fact that it appears at all is a bit of a mystery. It is obviously related to somehow to the AirPlay functionality, as the AirPort has been a playback target for sometime, since it was originally called AirTunes.