First off, fantastic! this will save me some dev time for sure. And the future option for adding multiple rows should open up some nice UX options.
However, I would definitely want to let the user enter data into a non-editable cell. In the old Table for cases where I wanted the user to be able to add an entire record, not just the editable ones I gave them, I was forced to create a separate form to do so. Of course that was SOP with the new table until you added this feature.
In the old table, rather than a new form, I was sometimes forced to make a column editable so that the user could add that value in a new record, but I would not otherwise want them to be able to edit the value later, at least not in this particular table.
One option is to have a new flag for each column called Show When New or something like that. It could default to true for any editable columns.
I also highly recommend having an onNew event in addition to the onSave event. Making me check .newRows to see whether I am running a Bulk Update or an Insert query is not compatible with the Retool Way IMO.