hi lukas,
photoshop is a concurrent to scribus (directly (you can't imagine how many people around the world are doing DTP with photoshop) and indirectly (as part of a suite which does DTP, among other things)).
as far i can tell, most graphics designers will think of photoshop when seeing your proposal.
on top of it, as you correctly point out, the feather is a symbol for "old hand-made books"... but scribus is for working on a computer and targetting a modern press!
i like the graphical part of your proposal, but i'm really convinced that we should find a branding which recalls the modern printing workflow, not the medieval amanuensis.
and this is not an easy task!
... and a blue feather is a no go! ... and i'm know what i'm talking about: we came to the same idea during a logo brain storming a month ago :-)
for what i'm concerned, your effort is very welcome! but your proposal needs some further work...
ciao
a.l.e