A exchange rate in the billions of dollars is possible if the dollar enters hyperinflation. In that case, the exchange rate of Bitcoin could reach billions of dollars. However, if inflation continues as it has so far with real inflation around 7 to 10 percent Bitcoin will likely continue to grow in line with inflation, and probably, after the halving in 2032, it will surpass 1 million dollars.
It is about million, not about billion but you are right about that in a scenario of Bitcoin price skyrockets to $1 million of dollars in a very short coming time. It will only possible to happen if the world has massive inflation in fiat currency supply and I don't want to live in such a hyperinflationary world.
A second scenario is Bitcoin grows naturally from development, technology, use cases, utilities, adoption then value and price. In this scenario, Bitcoin can hit prices like $1M without much big hyperinflationary problems globally. I would like to live in such world and have bitcoins in that scenario to get profit and retire a little bit ealier.