The question is very much arguable; many will present their facts and reasons for why they chose the answer they chose. Currently there is no asset that has proven to be competitive with Bitcoin, so we can say that Bitcoin will sit on that throne for a long period of time.
But we are in the era of change, where new impressive innovations are welcomed and accepted. If in the near future there is ever going to be a new asset that will fill in the gap that many consider to be very important, then there will be a shift in choice, but that's not going to happen anytime soon, not even in the next few decades, but in the near future we should be ready to accept change.
You really talked so genuinely. Some would say never, there is no going to be a replacement of bitcoin. Let's take that of US $ which has muchly been an interesting global reserve currency but today, even the US governments are looking up to diversify into bitcoin for their federal reserve because the $ is fast loosing values and same time loosing it global interests.
Likewise the gold, it has also been an utmost attractive point of commercial value for store of values but today it is bitcoin era and everyone governments and institution companies who understands the concept and possible evolutions of digital technologies believing the reality of digital assets are fast approaching to invest on it.
Perhaps other advanced assets ahead of bitcoin may come to existence because the world is free for developments that would be of the interest of the people but for now, it is unimaginable to figure what that asset to sideline bitcoin would be. That is get me agree with you that the dominance of bitcoin is going to last like it is going to stay in that first class asset position until then the one to overshadow it will be discovered. For now, let is assume it's an illusion until it is realistic.