I tried it.
One, I used the wrong bread. I used, I think, an Italian bread with sesame seeds on top.
It had a hard crust and a dense center so it was overpowering.
Two, I tried making it five different ways.
1. Sardines, melted Brie, thin sliced cucumber
2. Sardines, melted Smoked Gouda, thin sliced cucumber
3. Sardines, melted Brie
4. Sardines, melted Smoked Gouda
and based on ED's recommendation, and why the **** not?
5. Sardines, peanut butter, thin sliced cucumber
The the texture with the cucumber was totally ruled the show. I couldn't taste anything but cucumber, and the slices were very small and thin.
Without the cucumber; I didn't really taste the brie, but the Smoked Gouda flavor did come through, and though mild, the nutter flavor did pretty good with the fish. However, the heavy bread still stole the show (in a bad way). I think a much lighter, more delicate bread would allow you to taste everything, maybe even the brie.
The peanut butter was too overwhelming. That's purely subjective, as I'm not big on putting peanut butter on anything but jelly.
Note: I wasn't using the greatest ingredients, I was using canned sardines (in water). They were pretty mild. I like cooking fresh sardines, so that might be an idea, but maybe too much work for a sandwich.
I think, though, this might be more of a recipe for hors d'oeuvres than sandwiches.