I think a leash would have a possibility to interfere a bit with sliding strokes or extended paddle roll, sculling support, recovery techniques, or leanbacks . . . but might not be a deal breaker though. Maybe worth trying out variations [coaming, waist, wrist connections] to see what works best while really thrashing around, heh heh.
Paddle finish seems to typically be oil, but I see no real reason to eliminate a slight textured varnish finish. Personally, I would just use a hard ‘finish’ if I was concerned about paddle strength or abrasion resistance and wished to add a little appropriate [to a specific paddle issue] glass reinforcement.
And not too many 2 pc greenland paddles out there, although I do have [given to me] one with a fairly un-aesthetic stainless ferrule that I wish wasn’t there. I haven’t used it but it just seems counter to whatever looks and feels that a greenland paddle should be. If you are really interested in this, we could meet halfway somewhere and you could borrow it until things get more normal.
anyway, some ideas