I believe that Bitcoin is going to have first mover advantage in the crypto world for long time. This could lead to rise in price of Bitcoin and it can only be considered as a digital gold for storing value. But as far as becoming a mainstream currency, I think Bitcoin is going to fail big time.
Reasons why bitcoin will fail as mainstream currency:
Consider most of use cases where you need to use currency in daily life. For example, you are going to coffee shop to have a cup of coffee and now you want to pay using bitcoin. The very first problem is transaction fee. To pay for a cup of coffee, you need to pay a transaction fee that can be much more than the cost of coffee itself. Other limitation will be transaction time. No one would like to wait to check if the transaction was confirmed or not, and with time the transaction speeds will get slower.
All blockchain based solutions will be having these limitations for long term. So what can be the alternative for this? Currently, the only cryptocurrency working for the solutions of above problems is IOTA. It is designed to target instant micro payments with zero fee. It is currently in its beta and gaining huge traction as an open source project. It is based on TANGLE which is not a blockchain but based on DAG (Directed Acyclic Graphs) for transactions.
So, though Bitcoin keeps on gaining popularity (as the new investor doesn’t know about use cases and follow the hype), the adoption of bitcoin as mainstream currency will not be possible and the simple reason behind this will be huge transaction fee and time.