It's amazing seeing that as expected, the dream of actual AOT for WebAssembly is already dead and (at least in the case of iOS) will stay dead for the near future if not indefinitely because the fantasy of AOT was never actually feasible
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I wouldn't really say that they're moving away from it. Since Android 7 (Nougat), it uses a hybrid AOT / JIT compilation strategy in the default configuration. AOT compiled code for the bundled apps/libraries is shipped with the OS, and it starts with JIT for out-of-band updates.
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For 3rd party apps, it also starts with JIT compilation. JIT compiler is set up to output persistent JIT profiles that are built up over time. When the device is plugged in + idle, it will regularly do profile guided AOT compilation for everything without bundled compiled code.
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Since update installation occurs in the background due to the A/B update design, it will also recompile everything using PGO AOT compilation for system updates. This is just the default configuration though. It can be configured through system props and used in various ways.
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Default:
pm.dexopt.ab-ota: speed-profile
pm.dexopt.bg-dexopt: speed-profile
pm.dexopt.boot: verify
pm.dexopt.first-boot: quicken
pm.dexopt.inactive: verify
pm.dexopt.install: speed-profile
pm.dexopt.priv-apps-oob: false
pm.dexopt.priv-apps-oob-list: ALL
pm.dexopt.shared: speed
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dalvik.vm.usejit: true
dalvik.vm.usejitprofiles: true
So, disabling the JIT and using full AOT compilation is still completely supported. Using 'speed' instead of 'speed-profile' removes reliance on JIT profiles. Using 'everything' avoids interpreter for one-time init code, etc.
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GrapheneOS has build configuration changes to use full preopt even in development builds, disable the JIT compiler / JIT profiling and use full AOT:
github.com/GrapheneOS/pla
github.com/GrapheneOS/pla
github.com/GrapheneOS/pla
github.com/GrapheneOS/pla
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The drawback is primarily using more storage space for third party app installations. A/B updates result in the recompilation on major upgrades happening in the background before the update installation is considered finished and it gets switched to the active OS partition set.
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Performance differences are mixed. In some cases it's slower, but in others it's faster. JIT compiler can theoretically provide better performance but the way it works has bad performance for initial app installs before everything non-cold gets AOT compiled in the background.