Rules Book:
There is no limit to the number of different enchantments
that can be on an object, but each object or zone cannot
have more than one enchantment with the same name
attached to it at one time. This includes both hidden and
revealed enchantments. For example, you cannot attach two
Bear Strength spells to the same creature. It is possible that
both players may attach an identical enchantment to the
same target. If an identical enchantment is revealed on the
same target, it is immediately destroyed
This creates some interesting interactions if players unknowingly play the same enchantment facedown on a creature. I remember there being a discussion a while back about the potential for counter spelling given the interaction.
That sounds great! It sounds like such counterspell tactics would be quite useful against the most threatening enchantments. For instance, a build that depends on mobility could include a force hold or two for casting on its own mage!
The only problem I might have with this mechanic being used in such a way is that it seems very much like sympathetic magic, and that should be a Sympath's specialty if we ever get a Sympath in this game.
Also, doesn't this mean that if there were ever an illusionist, the illusionist's creatures would either have to be REAL creatures, or if they're enchantments, they would be destroyed if they entered a zone with an identically named illusion-creature? Then again, an illusionist would most likely have training in mind, so would probably have some access to illusionary position control try to stop this from happening. Something like weaker forms of shift enchantment or enchantment transfusion that only work on friendly zone enchantments—basically an illusionary "force push" and illusionary "force wave" respectively. That would be cool.
This looks like a really fun way to counter and it opens a door in my imagination to lots of awesome enchantment countering to help compensate for the worst enchantment weaknesses of certain spellbook ideas. I'm not sure how I feel about it thematically, though.