That's not necessarily true, since the consoles were designed for analog video and the output likely needs scaling/aspect ratio correction.
As soon as you're doing anything other than displaying 1:1 pixels, you need a considerably higher resolution display than the source.
The 3DS virtual console is a good example of that. Its display is 400x240 - perfect for older 240p games if you play them 1:1. But if you use aspect ratio correction the image is blurred significantly because the display's resolution is low.
1:1 on the left, 4:3 on the right.
Even if it looks wrong for some of these games, I could only ever play them in 1:1 on the 3DS display.
At higher resolutions you can use aspect ratio correction and non-integer scaling and it is barely noticeable.
After having bought used hardware in the past, it's such a hassle to do - because there are so many potential problems and very little recourse.
It's why this is probably not going to go anywhere for me, as I can't seem to find anywhere with new-in-box Wii Us any more, or new (white) Wii Motion Plus remotes.
Huh, you'd think someone at Nintendo might have realized that they could charge the gamepad via USB instead of including a separate charger.
I had enough trouble with external drives on the Wii U (an external SSD) that I wouldn't want to risk it with a pendrive if the system is reliant on that.
From reading up on the hack process, it sounds like you either need to run an exploit every time you boot the system, or run a risky hack that could brick the system if the drive dies. That seems like a lot of hassle.