This is awesome
One summer years back I worked in a plant genetics lab doing something not completely unlike this to isolate DNA. I guess the main difference would be in the purity and integrity of the DNA collected - you certainly couldn't use this method to get analyzable samples. The kits we used in that lab contained lots of buffer solutions, enzymes, and other chemicals to break down the cell walls, remove the proteins, and precisely isolate the DNA. At the end, you get a few micrograms of the stuff. I'll stick with the stovetop method from now on. It's probably not hard to modify this to get DNA from other things - certainly other plants - but what about animals? You would have a hard time getting a big enough sample to collect a visible amount of DNA, and it might be more fragile. I've never done that, so I'm not sure how the procedure differs.
Maybe one day I'll be outside poking around in the dirt and come across some fossilized amber with a mosquito inside. I'll take it back to my kitchen, pull out the blood from the mosquito and...