Edge cases make poor gameplay designers.
It's hardly an edge case. It's something for long-term players to work towards, and keep us going for a while. Content that, hopefully, we won't gobble up within the first few days.
I have personally never had a billion credits. Most I've had at any one time is 800 million. It'll take me a long while to build up the 5 billion.
But I've never really chased excessive credits.
Late-game content, I would argue, requires late-game levels of income.