This is a good question
- I have much the same thoughts.
EvoTech make good looking frame mounted crash bobbins that look like the will protect the top half of the bike:
These have a bar that goes through the space above / in front of the top of the engine to connect both sides for more rigidity - they connect to two frame mounts on each side of the bike.
Barracuda (and others) make a much simpler (and considerably cheaper) version that's just a single bolt into the frame each side with a bung on each end:
But like you say you need to protect the engine casings lower down too.
I added the KTM PP engine case covers - the small orange things that cover the clutch / stator areas - they aren't massive but they would be the point of contact if the bike went over.
There are others that might give a bit more protection down there like the ones from SW-Motech.
I've left the rear foot peg hangers on my bike as they would be the point of contact at the rear, along with axle bobbins at both ends.
Like you I haven't decided on a frame mounted option yet.
I like the simplicity of the EvoTech ones as they match the minimal look of the bike.
But I've had bars on other bikes before and they are reassuring to have, probably give more protection, probably are more forgiving to the bike in a crash - plus they are handy for mounting things - lights / cameras and such.
I just worry that large bars would look out of place on such a svelte bike like the Duke!