Will there ever be rivers in the game?

I hope so too but will probably happen when we get dynamic water.

I manually crafted a river for the place I am building but the longer it is the more small ups and downs it has in it due to the big difference in terrain height and the block nature of water.

I have a hunch that if rivers were added right now then they would look even more odd than the ocean biome. basically a river might look like a long and narrow lakes so they would have abrupt ends without any logical connection to other rivers, or lakes, or eventually terminating at an ocean. There is a new world type being planned called "Islands" which sounds like it would treat biomes as individual continents (large islands) floating in the ocean. This would make it easier to create a logical separation between continents and should seem more natural. At that point i can see rivers being added and actually looking nice. The current world type is basically one continuous land mass (which is why the oceans just look like large lakes with beaches and not real oceans. The island approach I would imagine mimic the way Minecraft (or real-life) worlds generate and have a more natural feel.