From the rulebook about enchantments:
"When you cast this spell, it creates a magical "matrix" on the target. At this point, it is not fully formed and exists only as magical potential, with no effect on the battle. When the spell is revealed later, the caster "completes" the spell by adding additional power. It is only then that the enchantment takes form and can affect the target." (my emphasis)
First, if this bit of flavor text was taken at face value then you could not target hidden enchantments and cards like [mwcard=MWSTX2FFJ01]Harshforge Monolith[/mwcard] would not be able to function properly, since were are now giving hidden enchantments traits (wrap your mind around that) .
Now story time
Spells always have subtypes, names, etc.
It's why you can't legally put two hidden enchantments of the same name on a creature, but IT CAN HAPPEN.
When I cast a bear strength on your creature I dont have to ask if the current hidden enchantments are bear strengths to make sure its a legal cast. If you then reveal a prior hidden enchantment on the creature that happens to be a bear strength, I don't have to remove my hidden enchantment even though I know its not allowed to be cast on that target, the rules are very clear on when and where you check for target errors.
Now that sounds funny because if you have a revealed bear strength on a creature it's an illegal move to put a hidden bear strength on that creature, but it's 100% legal for a creature to have two enchantments of the same name unknowingly.
The only defense you have at this point is the bit of the rules where you are not able to shuffle or mix enchantments. Order that they are placed is important for opposing traits and such so when some throws a free hidden enchantment down on a creature I would make a note or place a mana token on it. If, when revealed it is not a command thenthey lost spellbook points and an action casting it.
All things considered it is a minor issue at best.
Using your Naiya example, you can totally gamble your mind shield on the Naiya card. Mind shield is not a mandatory reveal. So when she casts an enchantment on your creature that's between you and Asyra. Mind shield also has text to allow it to function as an immediate reveal when a psychic enchantment is revelaed and
work accordingly.
Then you have instances like Izimbila. Her ability text is always "active" even though she is not resolved. Much like the X value issue where the ability text explains what that cost is she has an text ability that describs what additional subtypes, if any, she has. That's why a barracks or a lair can cast her.
<More on this later>
@Puddin
If you control a Familiar during the
Planning Phase, you may select a
spell for it to cast during the round. The
Familiar may have restrictions on the
types of spells you may choose. Place the spell face
down near your Familiar, and tell your opponent that
it is the Familiar’s spell. Only your Familiar may cast
that spell during the round.
It's not crystal clear but I would say no. It has to prepare what it is allowed to cast.