It's been a while since I used an IDE (instead of vim), but don't most of them support code-folding that provides a light gray bracket for a block of code (usually with a collapsible indicator at the top)?
Note vim can do folds too. (Not a commonly known feature, I only learned about it recently myself.) But the effect he wants is the literal bars showing indentation levels which I think some IDEs have... vim could fake it by highlighting the bg cells.
Or is the effect you want slightly different?