The only way that I see an altcoin replacing bitcoin is when there is a massive prohibition on bitcoin SPECIFICALLY
Oh! I see. I get your point mate. As I think of what you've said, I may say that's a possible way to knock down btc. If we assume that every government of all nation decides to ban the use of btc in their country but allow the remaining alts then it will surely die because the demand will be forcibly lost And most probably the ending would be ETH reigning as the new king. Well, that's only an assumption and very hard to put in reality so gor now BTC will stay and remain on top 
. or if another altcoin surfaces and improves all the areas that bitcoin failed to meet.
It will be the same IMO because of the impression which are engraved in our minds that alts/token was just made for Pump and Dump. Yeah! They will support it at first, create hype and other stuff but once they are do they'll go back again to the strongest coin in the market. I agree with you that bitcoin will remain at top for "now". but yeah I think a new crypto will be created that will replace the bitcoin for being top, because bitcoin didn't have a large scale update that will benefit every single user of it.
But who knows! Let's figure it out together and enjoy crypto adaptation into real world
