It amusing to watch all these bat guano insane Bitcoin price projections that just draw lines on a chart an completely ignore things like the size of the global monetary supply.
Say totally global wealth is about $500 trillion. With 21 million Bitcoins that's about 24 million per Bitcoin.
So if everyone decides that owning stocks, real estate, cash and bonds is stupid and wants Bitcoin, that's how much you have to play with. Sure, the whole world economy would cease to operate as people just trade coins instead of drilling oil wells and building hospitals, but there's your ceiling.
More practically even 1 million is extreme because people would have to start selling of productive assets at a discount to buy something non-productive, that can only go up if someone else does the same.