For table charts, it would a great feature to be able embed icons. The most common use cases would be symbols like up/down arrows. But nowadays it is very easy for include a wealth of free icons hosted on font-awesome for instance.
Also, if pulling from external hosts is a problem, you could also interpret html codes, which don't pull from any external host, and have quite many interesting symbols: see https://www.toptal.com/designers/htmlarrows/symbols/
And, while we are at it. Images could also be nice, although not as prioriary as icons and symbols.