Here's what I know for now (please forgive any inaccuracies or other mistakes as I'm reporting second hand but might have a few more spare cycles than those closer to dev.):
TL;DR: A lot of work has been done, but we are not close to actually having ARIS on Android in a publicly useful way. You may be able to help test, but do not expect to be advertising your game as on Android anytime soon.
Status: There is a build of the ARIS Android client on Github in two forms: 1) an apk file. If you have the right version of Android (5 and below), you should be able to download this file and side load it onto an Android device. I do not have any devices below 6 so my knowledge of any specifics from here out are not based on actual use. 2) The actual source code. This could be used by developers to continue working on this piece of software. It could also be used to build the software into a working apk, but the little I understand is that this alone would not help you get around the Android 5 as maximum version as there are material factors that have changed and would need to be accounted for under the hood. Unless you area developer, there doesn't seem to be a lot of gain to building yourself.
What does it mean to have ARIS on Android? If this software were complete and tested, this is how it would fit in with the rest. You would make games on the web, just like before, and there would not be a difference developing for Android or iOS, each client app would see the games on the server the same as each other. If the Android version were in a finished state, FD could submit it to the Play Store where any users might find it, just as we do with the iOS app.
Until Android is in a pretty finished state, it probably doesn't make sense to have a build be very public. I am hopeful that some of us here can be helpful in testing, hence availability in a slightly less obvious way than the Play Store, but it looks like we're still a bit away from that moment unless you've got the right OS. And AFAIK, development is not ongoing at this moment or is a trickle. It will require more money and time to get out the door.
How far away is it? I don't know. I don't think questions like that really make sense because until it exists, it doesn't yet exist. CASLS has put a lot of work into their build, and there's plenty that reportedly works. Getting farther doesn't sound impossible, but it's not free. And in some real ways, having Android is a detriment to ARIS. As each platform moves forward, the app has to keep up. Maintenance, let alone accommodating new features, is a real cost.
I'm looking for money for development and both would appreciate any help and be happy to offer help to other efforts. We've had a few conversations at summits about fundraising, but haven't gotten too serious. TBH I'm out of my depth.
This is a fantastic little tool, strange as it might be, and I'd like to see it go much further and bring more people together. In some ways, it has come together slowly and in pieces, but it is still here. There has been something of the ant and the grasshopper to it in my eyes. Many others have come and gone. I'm really thankful to CASLS for putting their time and money into this even if we can't yet taste it. We're closer to Android now than ever before.