To answer your question in one word: No
I don't think we need another LoTR clone when it comes to races (only humans, elves and dwarves) and TES wouldn't be TES without giant walking lizards and cats (especially giant walking cats that offer you 'sugar').
And when you say that krogan are original, they aren't really. If you look, you'll see that they are just another always chaotic-evil lizard-thing race. At least Argonians mix things up by not being a race of only chaotic-evil lizards that their only existance is to be minions for the evil guy hiding in a cave. That by itself makes them unique.
And khajiit are a little more original than what many games have when they mean 'cat-people'. When they say this, they usually mean 'people with cat's ears'. TES took it one step further and made them actual 'cat-people', minus the fear of water
.
So no, they don't need replacing.