They are dating! Kuroki apparently confessed after the competition they went off to at the end of the manga proper. He will also be moving to Germany, having passed the audition for a German orchestra, and...
he basically proposed!!
In front of everyone no less! but in French, so no one knew! when asking Tanya to go to Germany with him!!
I'm not entirely sure if Tanya will simply agree, however...she looked a bit stunned...and she might have something going on with her piano too. argh!! next chapter!!
(will comment on the rest of the chapter another time...)
edit (12-31): btw, my initial reaction was "woot!!"...but it was almost immediately followed by orz...Kurokin has to work on his emotional/romantic IQ!!