Wario is called Wario because his symbol is an "M" (Mario's initial) turned upside down. However, since Waluigi was created after Wario, they named him by adding the first syllable of the name "Wario" to the name "Luigi", but since Waluigi's symbol is an "L" turned upside down, this makes no sense at all. That's why I propose Nintendo changes the character's name to "Guigi", since an upside down "L" looks exactly the same as a capital "Γ" (Gamma), the Greek letter for the hard "G" sound).