amenity=library + ?
Maybe Key:books - OpenStreetMap Wiki with a suitable value ?
blind=designated
Maybe following the model of social_facility:for and community_facility:for, the key could be library:for. Although I’m not sure if there is any advantage in having a different key depending on the amenity type. But those two seem to have become fairly well established.
By the way, it seems the amenity=library tag isn’t particularly suitable for such libraries. Because they don’t have books for ordinary people, only tactile and audiobooks.
I see 40+ uses of the tag social_facility:for=blind in Taginfo and perhaps this is a more interesting tagging scheme.
I wouldn’t use social_facility.
It is a library. Someone looking for books will not look for a social_facility.
And if once in a while, some abled people go to a place that is not designed for their needs, it can be an opportunity for them to learn how to read Braille. 
To be clear, I wasn’t proposing literally using the social_facility tagging, I was just giving an example of a tagging format for describing amenities for specific groups of users that seems to have become accepted in a different context.