Emulator

I think a more pertinent AA-related thing to address would be transparency antialiasing selection. You can force it on, driver-side, with nvidia Inspector, but that's a rather hacky solution. (To be honest, though, I don't know what's exposed to Dolphin in that regard.) As it stands, alpha tested transparencies are always notably jaggy.
Besides, combining high IR and some AA goes a long way towards killing jagged edges - more MSAA won't have a difference comparable to the performance impact, and while SSAA does have a big difference, the performance impact isn't really worth it...
Of course, one could argue that if you really wanted crazy graphics you ought to lobby for higher levels of IR (6x! 8x! 12x!) with better scaling algorithms (Bicubic! Sharp bicubic! Lanczos! S-spline!) and post-process AA shaders (FXAA! SMAA!) applied before downscaling. (And at that point, I'd hope you have an option to save the unscaled image, too, so you can show everyone your haphazardly taken screenshots in 7680x6336.)

Performance is a separate issue. Most users don't care about performance if the game is running at full speed. Don't forget that it's not like PC games. The max FPS is only 60.

Also, it is not needed to combine high IR and AA. I'm using 2x IR and 9x SSAA and I satisfy with the image quality.

8x SSAA is in Dolphin under OGL, Is 16x MSAA a thing, I think CSAA is used in Nvidia as a replacement now?