The pure extracts are intranasally active. My buddy Eddie got curious and slowly and carefully went through a few mg of a mitragynine/7-HO-mitragynine mixture intranasally quite some time ago.
There's a good reason one hasn't heard much about it - the isolated alkaloids have not been widely distributed, thank goodness (why bother when you can sell "100X" bullshit to people for top dollar?), and the effects from the isolated alkaloids, regardless of method of administration, are less interesting than those from good old-fashioned orally ingested kratom
Insufflating anything but the isolated alkaloids seems pretty stupid to me.