Yes, many investors regret for not investing in bitcoin  because it would give them good profit, considering that they invested in right time off course. I bet that many investors that invested late are regretting for getting involve in it at all. It`s all matter of perspective, a point in time.
Gold is much more stable and has been known as the most precious metal for centuries, highly valued among the people. Bitcoin is different thing, its value is highly variable and unstable so people that are willing to invest put themselves in much bigger risk. If there wasn`t that huge last years growth in value I am pretty sure that not many investors would even consider bitcoin as some sort of investment.
I agree that people should do both, investing in gold and in bitcoin, spreading assets in their own regime.