but it's only useful, if the grid's origin relates in some way to the drawing, not the origin of the page
I disagree.
The whole point of having a grid - as it currently functions in Scribus - is that you can align things to the same vertical or horizontal. That's what a grid is for. To put it simply, rows and columns.
If the origin of the grid was related to the individual shapes then it would be useless for alignment between shapes as they would have their own independent grids with different origins. The grid, therefore - and see below for a caveat - must be universal to all shapes on the page. (You could, however, have a different grid on different pages - or spreads - like you can with guides.)
To think about it differently: In the same way, guides are not related to frames, they are universal to the page. If guides were related to frames - in the same way as you say the grid should be - then there would be the same problem. It's the guides that allow the layout for the page. The guides are not just for specific frames, they're for the whole page. It's the same for the grid. So both guides and the grid should be defined to the page, not the frames/shapes.
Guides are for the page, not individual frames. Grids are for the page, not individual shapes.
However, having said all that, there could be a good argument for shape-specific grids where you aligned shapes using the guides or the geometry of other things on the page but that would require much better snapping and alignment tools. And since we don't have those, the grid must be page-oriented. If we did get much better snapping/alignment tools then I'd be happy to reconsider my opinion in the future but I can only comment on the current situation. (If someone wants to start a separate discussion about the future direction of snapping and alignment then I'd be happy to chip in with some comments but I think that's even further out of the scope of this post.)
having a good snapping between nodes, lines & co is probably a better way of aligning things
I disagree (as Scribus is currently, but keep previous comment in mind).
Consider, for instance, the exercises in:
https://wiki.scribus.net/canvas/Bezier_Curve_Basics_-_Part_1_-_Simple_Geometric_ShapesHow would you draw any of those examples without a grid? Without a grid you would have to enter specific co-ordinates for each node and control point; a
very laborious task.
I'm not saying that the grid should be kept just because these exercises couldn't be drawn otherwise, but this is how you draw geometric shapes, with a grid. A grid is both a vertical and horizontal rule at the same time. You draw a shape in relation to the other points of the shape. That's how geometrical construction normally works. (Not always, but normally.) I realise that this sounds a bit like having a shape-specific grid would be better but without the better snapping/alignment tools it would not be.
Yes, we do need better snapping functionality (see above, in various places), but currently that is not a substitute for a grid. The grid is needed because it gives you a structure to work with, or to put it another way, a ruled substrate upon which you can work.
(Even with better snapping and alignment you can't do everything that a grid allows for. If you want to put a point at a specific place but there's nothing to align it to then you're stuck. With a grid you just put it where you want. Done.)
Dropping the grid altogether - without providing tools that would make it obsolete - would make Scribus far less usable for shape drawing and almost impossible for geometric work. People would say, "Here's an application that lets you draw vectors but it has no grid to draw them on. Wow, that's terrible. What other basic stuff doesn't it have? How much is InDesign again?"
It would be far better to pack the grid away into the Node Editor where it is useful and doesn't get in the way of the page layout. Once the grid is "inside" the Node Editor, it can then be worked on separately to the rest of the application.
I know that Scribus isn't an art application and I know it's not a CAD application, but it does allow the creation of vector art and geometrical shapes (whether by accident or intention is irrelevant, it just does). Because of this, and until it provides better tools, it needs a grid and that grid should be "inside" the Node Editor and it should be a page-related grid. The grid doesn't need to be improved, at the moment, just moved so that it's out of the way of the layout stuff.
I don't think I can make myself any more clearer on this issue.