I think you can invest on Bitcoin in 2019, but dont forget about the rest of important coins like Ethereum, Stellar Lumens, Ripple and even Cardano. I am sure that in this 2019 we will see good projects using their tokens and blockchains and we will start fogetting the Bitcoin stage, we could say that once the people know the real Bitcoin utility (just a simple coin with a blockchain behind) and people compare with the rest of coins, the new ones will be on top for the 2020.