Honestly retro is anything I have the ability to backup and preserve. Now that digital stores are the default if I can back it up. It's retro. Not much you can download and just have or not need an offline component.
I’ve kinda decided that at this point anything that can natively output an analogue video signal is retro. Which would include Wii U I guess. But yeah, PS3 and 360 are kinda retro at this point even though it feels a bit weird.