I don't think that bitcoin will be ever replaced by any other crypto currency as I don't see any competition to bitcoin at a moment and even in future bitcoin will keep on updating itself with the demand of people so its hard for any crypto to replace bitcoins.
For currently yes, but I'm sure someday there will be another coin that replaced the bitcoin. The main power of bitcoin is the first and most popular, most users, and supported other developers. But a big issue like taxes, illegal transactions, and the number of confirmation if not resolved then the user will run out.
Those illegal transactions are cannot be solved in bitcoin because of the anonymity feature of bitcoin and that is why the criminals are using and abusing bitcoin but we can't avoid that because even in our fiat money that is happening and there still a lot of criminals that using fiat to do illegal transactions. Those big issues that you stated can be solved in just a few months of development for bitcoin but those illegal transactions are exempted.