It's about usury - ripping people off by charging huge interest rates (think loan sharking) or huge margins. Sharia goes one step beyond this and doesn't allow people/banks/institutions charge interest at all on loans. Any funds would have to be socially responsible too. Ironically you would have thought that it would make investing in the oil industry tricky. Sharia banking has taken off in recent years amongst companies as they don't tend to gouge as often as traditional banks. When the 08 crash happened a significant number of companies ran to the Gulf State banks. Barclays of the UK, for example, got bailed out by Gulf banks.

A Sharia based exchange probably won't charge a percentage for trades but a fixed fee (maybe banded) or possibly a monthly fee.

Whether you like the idea or not it will help open up crypto to a significant number of people in the world which can only be a good thing.