Android is a highly customizable operating system but there are still some things that you can’t easily change. Almost ironically, the simplest customization, applying themes, isn’t possible without rooting your device. In Android 8.0 Oreo, however, developers have found a way around that limitation, creating the Substratum app and subsequent themes around it. Starting Android P, however, that workaround will no longer work and you’ll have to make do with theme engine your OEM has or, in the case of Google Pixel phones, none at all.
The whole rootless theming came about thanks to Sony’s pioneering work that eventually got integrated into Android as the Overlay Manager Service (OMS). Technically, it is the framework that would allow theme engines to work but that access was initially only available to OEMs or those with root admin privileges. But then some developers discovered that Android Oreo provided an ADB access to OMS, making it possible to have a third-party Substratum theme engine without rooting the device.
That will no longer be the case in Android P because as far as Google is concerned, that capability was actually a loophole and a security exploit waiting to happen. And like any such security hole, Google had to shut it down, despite user protests. Here’s the Android maker’s statement in full:
“We appreciate the feedback and would like to share some background information and clarifications.
The Overlay Manager Service (OMS) is intended for device manufacturer’s use. OMS, in its current form, is not designed to be a generic theming feature — more design considerations will need to be put into it in order to uphold Android platform’s security and product standards for users. Accordingly, OMS has never been advocated as a public developer feature.
Earlier this year a security patch (CVE-2017-13263) was released to OEMs for Android Oreo devices. The patch restricts the installation of overlays to pre-installed or system-signed apps, in response to a legitimate security issue raised in Android Oreo. Android P also includes this critical security patch, so it restricts overlays in the same way as does Android Oreo.
We understand that custom theming is an important capability for some users. We will take your feedback into consideration with any future work in this area.”
There’s a bit of a good news there that Google might consider such functionality in the undetermined future. Unfortunately, that is no assurance for those who have paid for Substratum and some themes and even less for its developers.