That will eventually include the Apple TV, though the current releases of i OS 11 and tv OS 11 do not yet support Air Play 2.
In the fine print on Apple's own website, the company notes that a firmware update may not be enough for some devices to support Air Play 2. Apple is partnering with major speaker companies for new, upcoming Air Play 2 devices.
While regular Air Play devices cannot be added as Home Kit accessories, they'll still work as previously, with an i OS device capable of streaming to one Air Play speaker at a time. Legacy Air Play speakers support this feature from a Mac, but not from i OS devices.
When I visit the firmware page, I don't see a download link, but when I follow the attached instructions, the only firmware options I see in the Airport Utility are ones that I have downloaded locally.But with multiple reports suggesting that Apple is exiting the Wi-Fi router business, it's possible that the legacy Air Port Express may not receive the necessary firmware update for Air Play 2.