400k is possible only if amazon, tesla, louis vuitton, big banks and other huge/rich companies, started to accept bitcoin. But that would happen for many years considering the fomo, even 50k is too hsrd to reach right now.
There will come a time that the exponential growth will slow down. And now that we have seen institutions and big companies entering the market, we can only say that the push is about $40,000 currently. So that will be like x10 to get to $400k, so more money is really needs. I would say that if there is a complete flip from gold bugs, we might see
BTC = 6 digits in the future.
$50,000 though is very easy to hit, as we might get there this year alone. But 6 digits or even more will be harder.