This has been argued many times so far, and we can't really say anything for certain. I mean if we are talking about 600 years from now, then looking at the human capacity for evolving, then we could say that it is guaranteed that there will be something better than bitcoin one day, there is no doubt about that. But I assume that we are talking about our life time, and I feel like it would be possible, but not certain. We could probably see some changes, which is why I do not put %100 of my money in bitcoin, well right now it is but if I ever have a lot once again one day, then I would not, and make sure I leave some room for something new in the future.