Yes and no, there are new APIs to support the same use cases, and none are standard/cross platform. Whether they are part of DirectX formally or not is not important.
While XAudio2 is a key library, it is not DirectX one, as we were talking about DirectX umbrella project. It is not as low-level library as other DirectX projects were anymore, it doesn't talk to the hardware directly. It is really just a user space library with convenient functions, made by Microsoft. It also has competition, there's OpenAL, which is similar - even if it doesn't have as nice API, it is cross-platform.
Yeah, I understand, that is why I said it is not DirectX, but being in DirectX or not is just marketing.
The reason is that XAudio2 (and lower level ones and other non-audio ones) is developed, distributed and recommended by Microsoft, and it is used by many major games and audio engines.
So I don't understand who cares about whether it is formally part of DirectX or not.
I didn't claim there aren't alternatives like OpenAL or Wine's XAudio2 implementation. I simply said the original XAudio2 is not portable on its own, which means you cannot simply use it in Linux, for instance.
These APIs were deprecated for more than a decade. DirectSound since cca 2008, DirectInput since 2002, DirectPlay since 2004.
The APIs that are left under DirectX umbrella are Direct2D, Direct3D, DXCore (adapter enumeration), DirectWrite (font rendering) and DirectXMath.