Ok we all love bitcoin 
, but there are hundreds of newcoins and not all of them are crapcoins. Bitcoin is the innovator and trailblazer but they are usually not the ones to succeed in the long term. What features that are improved over bitcoin will allow a new coin to ultimately dethrone the king.
1) faster transactions
2) Lower transaction cost
3) anonymity
4) premined pos which saves energy
5)
you get the idea
, but there are hundreds of newcoins and not all of them are crapcoins. Bitcoin is the innovator and trailblazer but they are usually not the ones to succeed in the long term. What features that are improved over bitcoin will allow a new coin to ultimately dethrone the king. 1) faster transactions
2) Lower transaction cost
3) anonymity
4) premined pos which saves energy
5)
you get the ideaNone of the above, strictly speaking.
The ultimate determinate will be net-work effect - that is the number of people adopting the technology having a snowball effect that brings even more into the fold.
Now exactly how this might be achieved... it's not likely that an open source alt-coin would spring up and overtake Bitcoin as any game-changing features could ultimately be co-opted by the developers into Bitcoin.
The only real threat I see is if the major banks and credit card companies somehow got together and created a closed-source cryptocurrency that had the same look and feel to the end-user that Bitcoin has. They could then put their global marketing machine behind it and if they did I believe that could represent a solid threat to Bitcoin's dominance.
They could also employ other dirty tricks such as making the use of their credit card processing services to a business conditional on their NOT accepting Bitcoin as a payment method.