Err I think we must be using two different definitions of the word mainstream. Of course not everyone who uses the internet is in my definition, considering where this discussion is taking place. Right now, though, anyone who uses bittorrent, IRC, anything else of that nature, will have no problem understanding newsgroups. You're really making the process out to be more difficult than it is.
Search for file on search engine, hit "Download message", let it open the program automatically and you're good to go.
Once download is finished? All that's involved is right clicking the first .rar file (everyone can count) and selecting "Unrar here". Okay, so now a .cue and .bin file is there. All they need to do is double left click the .cue file and the burning program automatically opens for them, ready to burn it.
But like I said, this isn't about them. This is about the fact that right now everyone who uses other means of obtaining larger-end items will be looking into newsgroups, because it couldn't be simpler to use. It's going to spike, and it's going to do so majorly, especially when some ISP's are giving out newsgroup access (limited to 1-2gb usually). All someone needs is a taste of this stuff and they'll never give it up.