Gadrial didn't utter an incantation, but on most of those few occasions when we have seen Magisters casting spells directly they haven't. Gadrial didn't make a sound, for example, when she stood between Shylar and a battle dragon and was suddenly surrounded by "a literal corona of light" and "fire seemed to crackle in midair three inches from her skin."
It seems unlikely to me, though that she feared that gifted would not be necessary. That is a political consequence and she isn't a politician she is a magical theorist. The level of fear she experienced and the speed with which it hits points to something she deeply knows, not something she doesn't pay much attention to.
Reading your posts, though I have modified my theory a bit. I currently think that on Arcana instead of being tightly tied to matter energy (at least kinetic and chemical) can easily and naturally transform to Arcana energy. This leads me to make several predictions:
1) Erosion is slower on Arcana because a measurable amount of the energy applied to rock on Sharona (or Earth) when water (for example hits it) transforms into Arcane energy on Arcana and doesn't affect the rock.
2) Any machinery that relies on storing energy in matter will have a problem on Arcana because some of that energy will turn into Arcane energy.
3) If this transformation process were to be disrupted Arcane motive spells would fail, for they relay on changing kinetic energy into arcane energy and vice versa for their effects. Note, this means the spells are much much less power intensive then I expected when I thought about them last.
I think it is effect three she saw and that explains her fear. If Sharonan beliefs, which prevent this change, become widespread all Arcanan physical transport spells will fail.
PeterZ wrote:One quibble that has major connotations. I don't believe she uttered an incantation. It wasn't necessary. If it was, Jathmar couldn't fire the gun. What she did was define the process and used her Gift to prevent aether from interfering with that defined process/spell inherent in the firing sequence.
What she feared is that magisters and magistrons would not be necessary. Recall that her fear is described as only a possibility even if this belief was widespread in Arcana.
It makes more sense to me to consider aether existing in the environment as interfering with much of the normal physical reactions. Since it reacts to mental activity, it follows that mental activity can inhibit that interference.
Otherwise, I think you are dead on.