Bitcoin is a decentralized currency It is very difficult to say whether such coins like Bitcoin will be discovery in the future. But in my opinion such coins will not be another discovery.
There is nothing impossible. There can be another coin that may be invented that will not make use of blockchain but decentralized and deflationary which will also be called a digital currency. But such a coin will have most characteristics that bitcoin is having and people may still call it an altcoin.
They created many altcoins and say their coins are Bitcoin killers but those coins die with time. Those coins fail to kill Bitcoin even you talk about Bitcoin Forks.
Bitcoin forked coins existed but they become not successful as bitcoin. That is true. Most altcoins are shit coins. But there are some like ethereum that supposed to be good but they are centralized nd become a security instead of been a commodity like bitcoin.