That's a fair assessment based on what I've seen and this seems like a fine solution to me. If you'd like, I'm willing to contact the Osage Nation to get their input.

An example is that I'd like to create an item for the Osage principal chief Baconrind, whose native name is transcribed by Carolyn Quintero in her Osage Dictionary as Wašį́haa. This is what is known as a "Siouanist" transcription, reflecting the way scholars writing on Siouan languages like Osage and Lakota have transcribed the languages in their works.

I don't have character support for the new Osage script and it's not the one I learned or the one I have reference materials in, so I'm unlikely to use it. I don't have a problem with specifying the script every time I use the language code.