Bircoin is a mature financial instrument now and we will see less and less price volatility in my opinion. The best strategy for getting profits quickly is to invest in altcoins and ICOs. As they still can grow rapidly. But the chance to make a mistake is also higher though

I don't think that cryptocurrency will be accepted everywhere by that time. The main barrier is that technology penetration doesn't happen so quickly. Even if some countries will allow payments by crypto, there will be still a lot of entrerpreneurs who has no idea what cryptocurrency is, especially in small towns. So I think it will take longer.