I think that Bitcoin has, in the mean while, gained traders' confidence. Therefore, it is though to threaten Bitcoin's existence while it has polished up the market of digital decentralized payment system. The least effect that too many Altcoins can do is to denigrate the market coverage of Bitcoin for a certain period, but Bitcoin won't take a long to recover its market coverage.
Although too many Altcoins cannot become a threat to Bitcoin, it scams are a greater threat while the more there are scams in Bitcoin, the more traders will lose their confidence on Bitcoin. Therefore, it should be under shield to reduce scams and strengthen its market coverage. Taking steps to reduce the number of scams will popularize Bitcoin in a great extent. So, Bitcoin's future depends on the reduction of the number of scams that are causing people lose their confidence on Bitcoin.