I was just thinking about that.
In recent pre-ATH times we saw two things:
1) Withdrawals of bitcoin from the exchanges.
2) Growing demand from institutional investors.
When people withdraw the bitcoin to their paper or hard wallet it is because they do not intend to trade with it, but to hold, and this reduces the offer. On the other hand, institutional investors don't buy 1 bitcoin or 0.1, they buy large amounts, making demand very high.
If this trend continues in the future, we may see prices that we now consider crazy, and even more so if we consider that institutional investors do not buy bitcoin to trade as individuals do.
Yep, it's quite a potent combination. The dynamic is worth mentioning because people try to apply rational ideas ("there is a limited amount of money, so for BTC to rise it must come from somewhere else, so BTC's market cap can't possibly be bigger than gold") to an irrational market. It doesn't work. With an extremely limited available supply, extreme and totally irrational valuations are possible. We're talking about the blow-off top of an exponential bubble. Market caps are not physical barriers.