Blue sky thinking about the ideas destined to become big money spinners is among the most creative - and exciting - aspects of investing. Predicting what the world will look like in coming decades is notoriously hard though, and even financial professionals often get unstuck when forecasting trends and finding the companies most likely to exploit them successfully. So, you need to keep your prophesy-making tendencies in proportion, and only allocate small portions of your Isa portfolio to niche themes. But if you do want to take the risk and do that, what might the future look like? We asked financial experts what sensible investors should consider before they put money into thematic funds, before doing some of their own crystal ball-gazing on what will make a fortune in the future.