Are placeholders supported in @CHUNK?
As of ContentBlocks v1.9.0, yes they are! :)
You can specify placeholders in the chunk name itself. That's useful if you have subtypes of chunks depending on a field setting.
For example the following field template:
Assuming "style" is a field setting with value "Card", ContentBlocks will parse that into the following chunk tag:
[[$CallToActionCard? &value=`Some Value` &layout_id=`5` &layout_column=`main` &style=`Card` ... ]]