Does it lack support? It says it supports various apps from the App Store or phone, so it might work.

I was surprised when I tried using Plexamp with Siri in my car and it worked (this was with the old Siri, not even the new one).

On the specs page it says:

Apps Available from iPhone:

- Audiobooks

- Classical Music

- News

- TV

Underneath that it says "Supported third-party audio and video apps". I'm not sure what that means.

But yeah! Plexamp works fine with Siri on my phone.