In a blow to the custom themers out there, Google has responded to the cry for Substratum "support" to return to stock Android. The verdict is that the breakage first spotted in Android P Developer Preview 1 is intentional and that it won't be fixed for the final P release.
Substratum, specifically the Andromeda project, is a method of installing custom themes on stock Oreo without root access — Substratum has long been a staple of the custom ROM community (and preferred over the CM Theme Engine). When people noticed that Google had removed the security hole that allowed Andromeda to work, several vocal people raised a ruckus, some going so far as to create a petition demanding that Google revoke its stance. Obviously, that didn't work:
"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.
Status: Won't Fix (Intended Behavior)"
So for now, custom themes are out of the question, unless you're on a custom ROM. Perhaps another exploit will pop up down the line, but it looks like installing a #HOLOYOLO theme on my Pixel 2 XL isn't going to happen. Sad day.
Understandably, the comments following Google's response are less than happy. I don't recommend chiming in over on the Issue Tracker since it really won't accomplish anything. Maybe Android Q will support Substratum, but I'm not holding my breath.
Alternate title: "We're not changing it, but we understand you're upset, thxbai"