Before suggesting them, I'd say list out the use cases for them. I've seen some suggestions, but none of them require adding anything to the programming languages themselves because they're about documentation which can (and should) be done separately from the programming language itself. Diagrams in documentation comments, for instance, merely requires Unicode in the comments and every language I know of supports that.
As a counter-argument, I'd suggest looking at APL. It did just this, using a myriad of symbols for operators and keywords rather than conventional text like most languages. That produced a language that was concise, elegant and utterly unusable by 99% of developers (the remainder not-jokingly referred to it as a write-only language due to the difficulty of reading and understanding even your own code, let alone anyone else's). Before going this route, explain how you're going to prevent the multitude of difficulties apparent in APL first.