Hi all, sorry to have caused any confusion here.
We are hoping to support custom properties in our default line items module soon. It is a highly requested feature so we are trying to prioritize this as soon as possible.
In the meantime, with the launch of customized quote templates, we are providing more flexiblily with default and custom line item properties than there was in the legacy quoting feature. I’ll make sure to update this thread once custom properties in the line items module is supported.