Is the feminine instrumental in -ою literary only nowadays?
1 Answer
It isn't only literary, you can hear it in colloquial speech and rustic dialect, and in phraseology and idioms. Or just to express you feelings brighter.
For example: "Я горжусь тобой" (I proud of you) - is just regular phrase, means exactly what it means.
But "Я горжусь тобою!" - has a lot of feelings inside, mostly warm.