Yes it can be used for long term investment but the price of 2 million per bitcoin is too high, it's possible but it will take time and the chances is pretty slim, but for sure it will be very profitable if we keep bitcoin for long term, there are some positive news that makes the chances of bitcoin grow big
Take a look at the early years of Bitcoin, no one can think it has reached over $18,000. $2,000,000 is a very high level but I think nothing is impossible, for a long time to come. I am investing in Bitcoin and I encourage people to do so in the long term.
Of course, Bitcoin will become a reliable and valuable store in the future. Maybe not for long.