Theming has always been a big part of the Android experience, offering Android device owners the option to further customize their experience. This was even more true when it came to CyanogenMod which placed a good deal of focus on its ROM users being able to make use of themes to not only customize the experience in general, but to do so at a system-wide level. However, the latest details on what was commonly known as the CyanogenMod Theme Engine (CMTE) is that it now seems to be in the process of being well and truly put to rest.
Following the demise of Cyanogen in its current form, CyanogenMod essentially undertook a rebrand and now much of what was on offer through CyanogenMod is available through LineageOS. However, in the most recent versions of LineageOS CMTE support was largely absent. Now it seems LineageOS has not only removed traces of the theme support at the user-facing level, but also at the code level. As a commit has been spotted for Android 8.0 (Oreo)-based LineageOS 15.0 confirming much of the code traces related to CMTE is also now being removed.
While this certainly seems to indicate the end of theme support, it does only seem to be a matter of clearing up what was already largely a process in motion. Not to mention, it is only really the end of theme support in its current CMTE form as there is nothing suggesting that theme support may not become available in a different guise and as more of a direct LineageOS labeled feature. Likewise, this is less likely nowadays to be a feature missed by many Android users as in spite of the drop in support for this particular version of themes, OEMs have been making theming much more widely available to their device owners. In addition, there are plenty of other routes now available for third-party ROM users to add themes to their devices, including for those who use LineageOS. So support for theming still continues, it is just that the once very popular CyanogenMod Theme Engine finally seems to be coming to an end.