It'll keep on going up after $100K, but it can't get infinitely big. Just as one upper bound on Bitcoin, the total size of all real assets in the world is less than one quadrillion dollars (to be specific, one million billion 2020 purchasing power dollars). This puts a crazy upper bound on the price of Bitcoin: $50MM. Likely, Bitcoin can't reach even 1/10th of that as a market cap ($100 trillion), as there is not that much demand for safe assets over all assets, so the highest possible price is likely $5MM per bitcoin.