Primary stat increasing augment runes are returning in The War Within, with the Crystallized Augment Rune. Hopefully they won't be quite so rare this time around!
First added in Warlords of Draenor, Augment Runes are consumables providing a minor increases to strength, intellect, or agility, similar to food buffs in not normally persisting through death but with the added downside of being much less widely available.
While previous expansion runes could be reliably obtained from Mission Tables or other expansion-specific activities, the Draconic Augment Rune of Dragonflight has been one of the least available in recent memory; only regularly obtainable from Draconic Satchel of Cooperation sometimes offered to tanks and healers queuing in the dungeon finder.
This kept their price prohibitively high for most players throughout the expansion, at least until the unlimited use Dreambound Augment Rune was introduced in Patch 10.2.
The single use consumables are typically replaced by unlimited versions towards the end of each expansion. With no information on how the new rune will be acquired, it's difficult to say whether the situation will repeat itself in The War Within, though following the trend of previous expansions, we can expect there will probably be a unlimited use version added in a later patch towards the end of the expansion..