Original plan about collections was to support dynamic overrides.
Collection would have been duplicated. Settings would have been different on each collection.
And each collection would have been the one displayed on its appropriated View Layer.
One View Layer used for lookdev and one view layer used for other type of work.
That was complicated to achieve and settle how every other basic of new 2.8 design should work, at same moment.
So, decision was made to focus on library overrides to replace proxy system for animation more than render management.
So, we are basically stuck with same limitations and abilities as before.
- Simplify panel in Render Properties
- Render/Viewport settings in Modifiers
- Geometry versus Material features
Plus the ability of geometry nodes to handle one node tree for viewport and another one for render.
For this specific case of a bevelled curve object, you can use bevel profile + a bevel modifier + use of bevel node for a Cycles render.