It's on pause at the moment, but will hopefully revisit it soon. Our policy is not to discuss when a feature will be complete, as it can be hard to predict and some people take our word as gospel. Sorry about that :/
What I can tell you is the current intention is that only the C3 runtime will support expansion APKs. So it would unfortunately not support your current project. It's unlikely that we will look into backporting support to either the C2 or C2.3 runtimes in the future.
If your up to the challenge you may have some luck exporting as an Android studio project and generating an AAB. There's supposedly some size reductions to be had just switching format. Failing that if your trying to reduce the size of an APK you can use a tool like 7-zip to see what it taking up the most space ( APK, AAB and C3P are all technically zip files ), and then optimise accordingly. I believe you can technically edit an APK directly, but you will have to manually align and sign the APK afterwards.
Here's a screenshot looking at an AAB I created yesterday, other than a few small tweaks they aren't that different from an APK. Looking through it I can see that 4MB of the 7.6MB for this archive is taken up by music, and 2.6MB is images.
I tried re-compressing one of those images with tinypng ( lossy ) and it went from 404KB to 146KB with no noticeable change. If all the images compressed that well the archive would now be 5.9MB. You probably have 2 versions of each audio track as well ( m4a and ogg ) but only need 1 ( ogg I believe ). If all the m4a files were removed that file would lose around 1.2MB coming to 4.7MB. Which is a pretty healthy reduction!
You can make these changes in windows explorer; directly to the android studio project. So you don't have to mess around editing an APK file.