Well, now that we have Mana Infused String, we have all the components necessary to build one of these. Also, due to Anvil mechanics, vanilla Fishing Rods can't be infused with Timeless Ivy. It'd be nice to have a Rod that doesn't break after a few uses. It could have some sort of bonus effect/buff/whatever, but that's not really necessary.

Maybe some fish that only it can catch?

Closing all misc ideas just to clean clutter, post them on reddit or the forums instead.