It would be also useful to have widget in 2D and 3D views (similarly to markups widgets interactors). It should be possible to set any position for center of rotation and should be possible to translate/rotate both in world and object coordinate systems.

See discussion here: https://discourse.slicer.org/t/set-center-of-rotation-for-transform-in-3d-view/14363/2

I'd really like an implementation that works as this one:

https://youtu.be/7RMermYOOYY?t=98

Please note that it has two modes:

1. One to modify the handles
2. One to modify the object

Others are invited to give their opinions

Could a roadmap of at least 5 steps be detailed?

Ooh, here there is already a discussion about it:
https://discourse.slicer.org/t/new-transform-widget-for-slicer/20483

Last project week I started moving the interaction handles from Markups and making them more generic, and adding them to Transform nodes. This is the branch that contains the changes: GitHub - Sunderlandkyl/Slicer at interaction_display_manager

@Sunderlandkyl I'm interested on implementing this, do you recommend starting from Slicer's preview release or your branch quoted above? :)