Not sure if this has been addressed yet (or in how much depth) in this topic, but here's how to get the Wifi addon working in Homebrew.
1. Once you have everything downloaded onto your SD card, follow the directory X:/projectm/launcher/addons, and you should find a .7z file named wifi.7z.
2. Use
7-zip to open it, and replace the files that show up (mu_menumain.pac, sc_selcharacter.pac, sc_selcharacter2.pac, RSBE01.GCT, and info.xml) in their respective directories, X:/projectm/pf/menu 2 for the .pac files, X:/codes for the .gct file, and X:/projectm/launcher/addons for the .xml file.
3. Load up the game via the launcher in Homebrew and it should work.