A mode for adding new points and modifying a closed object according to those points (e.g., click and continue to drag) would be particularly helpful for edge manipulation and object fine tuning.
The 'mode' aspect would enable an on/off and/or momentary on/off, e.g., where a control key is also pressed.
The issue of straight versus curved segments could be solved in the same manner, e.g., select/control key/other mode control with a potential option (e.g., default) to copy an existing point attribute, a selected point attribute and/or a last point attribute.

digimediaman wrote:A mode for adding new points and modifying a closed object according to those points (e.g., click and continue to drag) would be particularly helpful for edge manipulation and object fine tuning.
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What's wrong with Inkscape's node tool?

For more information, please read the detailed section in the Inkscape manual:

• Inkscape » Paths » Editing Paths: Using the node tool