apart of games which ipads also wont replace
The world isn't black or white. In order for something to be good or bad, it doesn't have to eliminate or "replace" other options.
iPad gaming is already much better than PC gaming on various parameters, for various reasons. 1, portability. 2, form factor and ability to use the gyroscope, built in cameras, etc. 3, better dev tools and a growing, vibrant ecosystem. 4, the power of the hardware. It is way more powerful than the vast majority of computers, out there.
Of course, it won't replace a built in tower for those specific AAA games that truth be told aren't even that popular for the die hard minority of PC gamers. Even with that minority, the majority plays LOL, Dota, Overwatch, Minecraft, CS Go, etc.
Personally, I don't have and I don't care about an iPad. I have a Macbook Air since 2011. But the 90% of people that carry around cheap, old, slow 7 pound computers? Yup, they dream about it.
Anyway, If somehow someone makes a Civilization quality game for the 12.9" iPad Pro, I'm willing to sell my soul to the devil for it. Civ's UI would be easy to implement on touch based devices, and I'm sure the iPad could run through Civ 5, but maybe not at default resolution. Anyway, Civ 4 would be so fucking awesome.