I would totally use them! I like computers and electronics and that kind of stuff, and it would be awesome to have Mario adventure through a computer. And I'm lazy AF, so I'd never really want to draw Windows tilesets myself for use in hacks. I wish Windows tilesets got accepted. I also saw that tiles from ZSNES' user interface appeared in one hack. I really like that for some reason.
Tilesets from websites like YouTube, Reddit and even SMWCentral would be cool too.
And adding to the graphics-that-I-would-totally-use, why aren't there actually any Undertale GFX besides fonts?
"Glauben Sie nicht alles, was Sie im Internet lesen." - Karl Marx