I hate to be that 'other voice', but knowing that you plan to feather back this beauty, I'd fill that hole with epoxy mixed with brass powder. It would shine like gold next to those metallic looking feathers!
...and to take the contrarian point to it's fullest, I cannot imagine that filling the hole would be functionally the same as not filling it. Air has nearly ZERO compression strength compared to just about anything you might use to fill the hole. Now, it may not make a difference that would ever be noticed, assuming that the wood around the knot never gets loaded up significantly. But if the wood around the hole would ever be stressed or move at all, then a filler that could push back and support the wood fibers around the hole would have to be better than ambient air to keep things in place. Am I missing something obvious in my thinking about this?
I suppose there is also the weight of the filler to consider, but that would seem to be a minimal consideration for performance.
OneBow