They do not even need to do much - glyph of Ascendance that lets you keep your character’s appearance with just additional colours / animations already exists in the game.
Blizzard could improve these animations and add a bit more visual effects to them - surrounding lava for Flame Ascendance, surrounding winds for Wind Ascendance and surrounding water currents for Water Ascendance, but at the very least could just return this glyph as an option.