In the Season of Discovery Phase 3 Preview Video, Blizzard unveiled some Rune Abilities coming in the next content release.
Blizzard heard your feedback that Runes in Phase 2 didn't feel accessible until level 40. They're looking to balance that with a mix of runes you can obtain while leveling but still have some to look forward to at the new level 50 cap.
There are still more runes to be officially revealed, as every class will receive six total in Phase 3.