I have an outline for a story that's been percolating in the back of my brain for decades, but never considered it as a screenplay for a film so I never considered it for casting.
I don't think the best writing comes with a single actor in mind, it should transcend any individual actor. Who might be good in the role now likely wasn't even born when I first had the idea.
You look at something like the Gunslinger by Stephen King, pretty clearly a Clint Eastwood archetype when it was written, but who fills that role now? One of the Skarsgårds maybe?