The fact that it generates a Nova means that it's ability is relevant in Rainbows. If it's ability is unused, then an Archangel it's better. So, you must sacrifice: 5 attack, 7/6 quanta to generate 12/24 quanta. Isn't better to take another Nova/SNova in the deck? (if you already have 6, then i think a quantum pillar is better because the combo is long, and you need quanta fast). If you use the ability only when the creature is going to die and you know it, the thing becomes too situational.
So, my suggestion are:
1)Make it a passive ability, so if it dies it automatically become a Nova/SNova
2)Decrease the cost from 5/4 to 4/3 and lower stats by 1 (so you can play this and Sancutary)