Just saw this post now, thanks for reviewing some of my Android pulls before.
I've been building Swift master natively on Android in the Termux app about once or twice a month and submitting pulls for the entire toolchain back upstream. I'm down to 11 failing tests from the complete Swift test suite you mention above, one test in Foundation that you already submitted a pull for, swift-corelibs-foundation#2145, and one test in XCTest and three in the Swift Package Manager related to Android incompatibilities that aren't important (Bionic doesn't support module maps yet, for example).
Otherwise, I have libdispatch up through sourcekit-lsp passing their tests on an Android AArch64 device (I don't really try ARMv7 since it's dying off) and have built and tested a pure Swift library package using just the package manager on-device. I will be submitting a pull to the Termux package repo for a Swift toolchain on native Android soon, already got a couple more Swift pulls related to that in the pipeline.
I can pitch in on the AArch64 CI, helping make sure it stays green. I don't know the extent of Android support in Azure, but with AArch64 support in cloud/CI services increasing and something like the just announced Anbox Cloud for Android, it should be possible for a company using Swift on Android to set up much more comprehensive CI, maybe using the native Android support I've been adding.