Make the internal SD card storage act like normal Ext4 storage (with file system permission management)
You seem to be missing the point. Actually a few of them:


Emulated SD Card storage has nothing to do with the lack of physical SD card support by some devices.
It is a public storage area by design.
It is implemented via FUSE - it is not an actual block device and you can not simply reformat it to any filesystem you want.
Being able to share files via MTP depends on the current implementation and the change like you are suggesting would break it.