I like the idea of "complementary set of keyboard shortcuts" :)
So,
Here are my proposals for Scribus/Inkscape shortcut unification as well as some random usability notes. Disclaimer: I haven't used Scribus much and may be unaware of some of its capabilities or limitations. This is a "fresh eye" look of a newbie. Disclaimer #2: I'm obviously biased towards Inkscape; feel free to argue if you think some of Inkscape's approaches are unapplicable to Scribus, or if you think Inkscape must borrow something from Scribus and not vice versa. This is only a beginning; if you like this I'll have more :)
All this is based on Scribus 1.2.
== Random usability notes (and one bug)
There are no tooltips on buttons, which makes them hard to figure out.
You have "Grab radius", but you need to also implement "Drag tolerance" as in Inkscape. This means that a mousedrag less than the tolerance pixels is considered a click, not a drag, and does not move an object. I use a tablet with pen instead of a mouse, and with a pen it's very difficult to make a precise click; it's almost always a small drag. So without drag tolerance (4 pixels by default in Inkscape), it's very difficult for me to use Scribus - trying to select something always moves it a bit, very annoying.
"Duplicate" shifts the new object a bit. In Inkscape we decided that it's a bad idea overall, so our Duplicate places the new object exactly over the original.
Consider using more explanations in the statusbar instead of the unhelpful "Ready". For example:
- the number and type of selected objects
- the reasons why some command fails
- explanations for the selected menu item when you go through the menu
- most common functions of Ctrl, Shift, Alt in the current mode, while they are pressed
In "Manage keyboard shortcuts," resizing does not resize the list, only adds empty space to the dialog. Also the size/position of the dialog is not remembered.
Calling e.g. Distribute/Align dialog when less than two objects selected silently fails. It must at least display some explanation in the statusbar. Better yet it must open but have its controls disabled until I select something to align. By the way the dialog is called simply Align, and the Distribute option seems to be always off - why?
Open the Script console. What to do? I type "help". It says, use help() for interactive help. OK, I type "help()". Scribus freezes.
== Most needed keys
Keypad +/- to zoom in/out (even in text edit mode! you have regular +/- for inserting these chars, so keypad ones should be zoom-only)
Middle-drag to scroll canvas
Tab (except in text edit mode) to cycle select through objects
Esc to deselect
== Arrow keys
You have arrow-key movement of objects, but here's how it might be made more rich and Inkscape-like. I think the Inkscape system is logical (again, I'm biased, since I designed most of it myself :)
Without modifiers: move by some predefined amount - this seems to work, but I could not find how to set that amount in prefs
With Shift: move by 10 times the predefined amount (seems to work, but I'm not sure if you use the 10x multiplier)
With Alt: move by 1 pixel at current zoom level - very convenient! (now the same as without modifiers)
With Shift+Alt: move by 10 pixels at current zoom level
With Ctrl: Scroll canvas by some pref-settable amount of pixels, ideally with acceleration as in Inkscape (now it moves the object by some small amount).
== Selector modifiers
The "selector" tool (arrow) would benefit from more Inkscape-like features:
Shift+click to toggle selection; you have it adding to selection, but more useful is to have it add to selection if not selected and remove from selection otherwise
Ctrl+click: select in groups (without ungrouping)
Alt+click: select under (cycles thorough z-order at click point, try Inkscape CVS to see how it works)
Note: ctrl, shift, alt can be combined
Ctrl+drag to rectrict move to hor/vert (this one is very important)
Shift+drag to force rubberband (selection lasso rect) even if starting over an object; add objects within rubberband to selection
Alt+drag to force move of the seleced object no matter where you start the drag
== More default keys in the "Manage keyboard shortcuts":
Shift+Ctrl+s Save as
Shift+Ctrl+d Document setup Shift+Ctrl+a Distribute/align
Shift+Ctrl+f Colors (?) Shift+Ctrl+t Fonts (?)
Raise/Lower/Front/Back: we use PgUp/PgDn/Home/End, but since you are more often in text edit mode where these are motion keys, what about using the same keys but with some modifier (Ctrl, Shift, Alt?)
Show grid/Snap to grid: we enable both with one key, since hardly anyone will need to see a grid without snapping to it. Our key is #, you could use e.g. Ctrl+#.
== Tools
By tools I mean the buttons on the toolbar that starts with the arrow button. Due to the lack of tooltips, I will have to describe which tool I mean instead of using the correct term, for which you'll have to forgive me. These tools are likely to be switched often, so they need keys too (if they already have some keys I could not find them). Here are the keys Inkscape uses for approximately equivalent tools:
"Arrow": F1
"Rectangle": this is a collection of shapes, but since the rect is the default, this would be F4
"Star": Shift+F9, the keypad * key
"Rotate": if you use a separate tool for that, it may be some variation of F1 (e.g. Ctrl+F1)
"Zoom": F3
"Text edit": F8
Other tools might use the remaining F keys with modifiers.
== In text editing
Visual adjustments in text are very convenient with these keys:
Alt+arrows: kern the next char by 1 pixel at the current zoom, both vertically and horizontally (try it in Inkscape to see what I mean)
Alt+>, Alt+< increase/decrease tracking in the current line (or in selection, when we get selection implemented), so it's expanded/contracted by 1 pixel at the current zoom
Ctrl+Alt+>, Ctrl+Alt+< increase/decrease line spacing in the current text object (or in selection), so it's expanded/contracted by 1 pixel at the current zoom
Same keys with Shift act by 10 pixels.
By the way, I could not find a difference between tracking (=letterspacing) and kerning in Scribus (maybe I missed something). In Properties I only see kerning and linespacing but not letterspacing. I know you can select a fragment and "letterspace" it by assigning kerning to it, but it's a bad workaround because it will lose any manual pair kerns that were there. SVG supports both letterspacing ("letter-spacing" CSS property) and kerning (dx/dy attributes on text) independently, and you need to support both if you want to import SVG text properly.