Runes can target and be attached to any permanent, even one that isn't currently a creature or an Equipment. You can cast a Rune choosing a Vehicle as the target, for example. The Rune's enters-the-battlefield ability will trigger, and you'll draw a card. The Rune won't do anything while the Vehicle isn't a creature, but if it becomes one later, the appropriate ability will start applying.
2021-02-05
If the target of an Aura spell is an illegal target as that spell tries to resolve, it won't resolve, it won't enter the battlefield, and none of its enters-the-battlefield triggered abilities will trigger.
Enchant permanent
When this Aura enters, draw a card.
As long as enchanted permanent is a creature, it gets +1/+1 and has trample.
As long as enchanted permanent is an Equipment, it has "Equipped creature gets +1/+1 and has trample."
