Instant transactions and no fees at all. Those two are prominent features that need to be implemented to bitcoin. Bitcoin(crypto) is not applicable for a canned transaction because it takes too much of your time, and the fee will be too large for a micro-transaction. For me, those are the 2 features that need to be upgraded.
Majorly what is lacking is mass adoption. We still have countries setting up regulations against cryptocurrency, Some persons are still skeptical about the genuineness of crypto. While some sectors like Financial sectors, Oil and gas, Agricultural sectors etc are beginning to adopt the use of blockchain in their services. Others are still skeptical. I sited mass adoption because until we can easily exchange Bitcoin or other altcoins for goods and services, only then will other things fall into place.
Mass adoption plays very important role in the success of digital currencies. The major reason behind this is not that people find it difficult to believe in crypto coins but that most of the people are still unaware of their existence. Obviously, we cannot explore what we have not even heard about. Anyway, things are getting better as digital assets are gaining fame gradually. It wont take long before bitcoin and altcoins will serve the purpose of currency.
Crypto is too advance for mass adoption, Imagine not all of us are technology literate. And not all of us have devices and money to avail the internet data for daily use. Those basic needs to use crypto are what stopping an average person from using it in their daily lives. The price is too unstable to serve it as a "normal" currency. Personally, I consider it a form of investment like stocks in the stock market. But who knows what if, in the future. Someone is going to create a coin that will satisfy all of the features that we are looking for. But for now, I think that will not be the bitcoin or any other altcoins.