I don't fully agree; Back in the '60's in Australia & England, knee length Cloaks were in fashion for men, and actually looked quite smart with a suit. I reckon a Fly Plaid could look fine, it is a somewhat dashing garment, after all.
We're all just so used to seeing it with a Kilt, and think it would look odd any other way (to us Kilties).
I reckon it would certainly add a unique touch. Try it and see how it looks - if no good, you can use it as a throw rug over a chair, or table cloth in the Dining Room.
And welcome from North Hollywood California.