When it enters play, you have to reveal an Elemental card from your hand. If you don't, Primal Beyond comes into play tapped. That's usually not going to be an issue in the right deck. Primal Beyond allows you to tap it for one colorless mana - especially useful for the new Colorless casting costs of the Oath of the Gatewatch Eldrazi. In addition, Primal Beyond can tap for any color of mana, but you can only spend it to play Elemental spells or activated abilities of Elementals.
The best application for this card is to help cast Horde of Notions or use its 5-color ability to cast any Elemental card from the graveyard. But even in a two color deck like Omnath, Locus of Rage, who has plenty of Elementals in his own horde, this can be a helpful color-fixer.
Other Commander decks that may be able to use Primal Beyond include Animar, Soul of Elements and Maelstrom Wanderer. In the case of those two Commanders, though, there may not be enough Elementals besides themselves to be worth including this niche land. Still, it's a good option to keep in mind if you're looking for inexpensive ways to upgrade the mana-bases of Elemental happy decks.