That's a shame, would've gotten Altiverse Spiritual Boxes and Mileage if I came back sooner than just a week ago.
Why was it discontinued? Will it be replaced with something else?
The level up rewards were discontinued as some players were exploiting the rewards through power levelling alternative characters.
At the moment, the only information provided in regards to the replacement of level up rewards as achievement rewards is found in this month's patch notes.