I guess that if exporting below Android 5.0 is not available it would be for some reason, but...can we expect it in the near future?
My cellphone, for example, is a mid-tier one running on KitKat, it can play pretty much any game, and to this day I never got any android version incompatibility with anything I ever tried to download from the Play Store (Well, as a matter of fact, I actually had that problem with Super Mario Run but the very next day I tried again and it downloaded and ran just fine).
As cool as directly exporting apks is, this is kind of dissapointing and greatly reduces C3 scope.