We have planning for Asset Variants feature. Which will generate different formats out of assets to support different platforms benefiting from best suitable formate on specific platform.
That includes textures and audio.
Although this is in backlog currently and we don’t have estimate when we are going to implement it.
Technically speaking, we can allow uploading m4a files, and they just should work with little improvement in engine and editor to support that. Then it will be your code to choose which asset to play ogg or m4a based on what is supported on platform your app is running.