This depends on: #842030: Create a line item add / edit form (or use a view)
Once there is a line item add / edit form, we can alter the line item table on the line item manager widget to have a more dynamic approach. Using a View, we could use a display plugin that for the label, quantity, and price we would load in the line item form via AJAX and submit that part of the form inline. There would need to be some visual indication that data is being saved as you modify it... Bojhan didn't really care for the approach of switching from plaintext to a form and back again for editing... so perhaps the values would always display as form elements and we could flash the background of the cell or something to indicate saved data. Any thoughts on that, Bojhan?
See the present form:

Comments
Comment #1
Bojhan commentedWell since we discussed it in person I agree with the approach you propose, talk to Damien about the flashing he has a script for that - as we discussed it earlier. Requires some tweaking but should be good enough of an indicator
Comment #2
recidive commentedThe patch #944640: Shopping cart as a view is a step in this direction. When this get in, I think this patch would be reduced to adding a price edit view field and an area handler with the widget to add line items.
Comment #3
rszrama commentedI'm going to actually close this one out as a won't fix. Changing this to a View won't solve the underlying problem of needing to change the validation / submission logic for adding and editing line items. Instead it needs to function more like the Inline Product Form widget, deprecating this approach.
See #1181862: Design the widget