Looking at the patch (not the code itself)... not sure if this a feature to implement or not. I understand that use a different camera can be useful, but my concern is to create a different workflow here that can be solved with the normal Blender workflow... why don't switch the camera using a marker.

In general IMHO we should try to create "custom" solutions for LineArt ... I know 2D has its own requirements, but we should avoid creating a set of workflows that need to be made totally different for LineArt. I know the easiest way is to just add a solution for GPencil (I had this situation many times these last few years), but we have to keep Blender's overall design view and how it can be solved using standard workflows.

I would like to hear the opinion of @Matias Mendiola (mendio) @Daniel Martinez Lara (pepeland) @Pablo Vazquez (pablovazquez)

In D12047#311249, @Antonio Vazquez (antoniov) wrote:

why don't switch the camera using a marker.

There are cases you want to have multiple camera's result shown at the same time, hence you want to specify a custom camera as there will only be one active camera at a time. Marker switching is already supported.

In general IMHO we should try to create "custom" solutions for LineArt ... I know 2D has its own requirements, but we should avoid creating a set of workflows that need to be made totally different for LineArt. I know the easiest way is to just add a solution for GPencil (I had this situation many times these last few years), but we have to keep Blender's overall design view and how it can be solved using standard workflows.

Yeah... This patch is because it's very easy to specify camera in line art, and adding this option provides quite a bit flexibility, while it doesn't necessarily have much big impact on existing workflow.

There are cases you want to have multiple camera's result shown at the same time, hence you want to specify a custom camera as there will only be one active camera at a time. Marker switching is already supported.

Yes, but this is the point ... how do you do that if you want to render a mesh (not GP) with different cameras? you don't use an custom prop to set up a custom camera ... just try using markers and repeating the rendering or duplicating the animation. My point is to stay consistent (I'm not saying your idea is bad).

@Antonio Vazquez (antoniov) Humm... yeah maybe I need to think about it 🤔

Actually this function is pretty crucial if we want panorama camera emulation. In which cases there will be 6 cameras rendering the same scene for the same frame for anything >180 deg (like sky box, though rare, but very likely 2 or 4 camera stitching for this kind of use)

Another use case for this is temporal stability, when you want to animate the actual camera but keep the lines stable by generating them from a fixed camera location. We have a dicing camera for similar reasons in Cycles, so it's not that unusual a workflow I think.

For panoramic cameras it would be good to support those directly at some point, so you don't have to set up multiple cameras. The next major Eevee version is planned to support them too. For line art that would require porting the Cycles panorama projection functions to the Blender camera code.