Elemental Mage was a strong budget options upon its initial release, but saw relatively little competitive play. It was mostly used as a tempo deck that would seek to increase board presence turn after turn by playing increasingly strong elementals that took advantage of their battlecries.
Rastakhan’s Rumble is looking to bring the archetype some new interesting elements to bring it to the mainstream of the meta. Elemental Evocation is a Innervate like spell that will help you bring out minions quicker and ahead of the curve. It is also useful for covering turns where you might not have a good play. Scorch gives you a potentially cheap removal option that can help you clear the board and keep your minions healthy. There’s also the big Jan'alai, the Dragonhawk which while isn’t an elemental itself, can help bring to the board the most powerful of elementals in Ragnaros the Firelord.