Just today I had a couple issues with Excel if I wanted to save something as JSON or if I wanted to save something as an UTF-8 encoded CSV (Excel converts it to ASCII).
One thing that would be simple and useful is the ability to generate or convert between different CSV file formats. For example, French CSV files use semicolons instead of commas to separate values, and use commas as decimal points.
Here's another problem: how do you make a field in a CSV that when you convert the document into JSON, the field becomes an array?