I'm not sure there's virtually any use for a billion bells if we're speaking strictly in-game, no villagers or anything. Even houses don't require that much.
this is what I was mostly wondering about. simply what is the point of having all that money in the game? it seems there's a badge you get for having 100 million, but besides that...I worry the game would become boring having such a crazy amount of money. no saving up to buy anything and maybe it loses that special feeling