Since there were no elf monks in reality I'd say it's impossible to use that as an argument for (or against!) "reasonability". You can't cherry pick a historical fact and then just apply that to the highly fictional item "elves are born proficient in blades"...
I think perhaps you meant to say "I consider it reasonable for racial weapons to be included in the monk weapon category, for little other reason than I think that would be awesome"? If so, that's something entirely different and I would wholeheartedly agree, per Rule as Fun! Go ahead, knock yourself out!
What I am trying to point out here is merely that there is
a reason monk weapons exist as a thing in D&D 5E. It makes no sense to suggest martial weapons and especially blades if you know what this reason is. So if you want elf blade monks, fine by me, it won't wreck anything, but please don't try to justify it with history, since, well, if anything, history suggests to us
the exact opposite!
Good luck with your gaming