In the new beta, the AirPort Express appears when attempting to add an accessory in the Home app. If you tap it, an alert is displayed which reads:
AirPort Express Update Available To use AirPort Express with Home and AirPlay, an update using AirPort Utility is required
There isn't an update to the AirPort Express available quite yet; however, this could be a sign that Apple is planning to recognize the device as a speaker option in the Home app. Back in iOS 11.4 beta, the device also appeared in the Home app but selecting it did nothing.
Apple SVP Craig Federighi told us a nearly a year ago that he would keep "in mind" our request to bring AirPlay 2 to the Apple Express and we're still hopeful that the feature will arrive, despite the discontinuation of Apple's router lineup.