- Classical Kanembu is still used and written by Islamic scholars of the area - although, apparently, Western scholars only became aware of this fact quite recently.
- It has substantially more cases than modern Kanuri, and possibly an even more complicated verb morphology.
- Most strikingly, since vowel length is non-phonemic in Kanuri, it seems to use vowel length to indicate high tone instead; thus, for example Arabic al-'aakhirah "the afterlife" has been borrowed as laxíra, and thus gets spelled as لاخِيرَ. As far as I know, this would make it the only Arabic orthography to mark tone. (Actually, Dmitri Bondarev, who observed this, prefers for the moment the more conservative interpretation that the vowel length commonly corresponds to a modern Kanuri high tone, not ruling out the possibility that such vowels were actually long in the Kanembu of the seventeenth century.)
This already constitutes some of the oldest documentation of any West African language, and quite apart from its implications for the reconstruction of Proto-Saharan, it really makes one wonder what other valuable historical data on other African languages linguists might be missing out on by not studying Arabic/Ajami use. So keep your eyes peeled, and tell me if you spot anything!