Only one major update and a few minor updates
Motorola promised only one more major update for Moto E. And I suppose, that one update will be for Android 5.0.
Android 4.4.3 has some bugs with openssl modules. Hence, Google made an unexpected update of Android 4.4.4 to fix that security issue.
So probably, we can get directly Android 4.4.4 update and then Android 5.0 update.
And future updates for better Android versions will be provided by developers.