As of now, there's no other champion with direct interactions to Zaahen. Dialogues from other champions are my personal choice of their voice lines.
I'm expecting that Riot adds some direct interactions for those who are important to his lore such as Xin Zhao and Yunara. (and hopefully Darkins...)
I was going to sleep and but I noticed that Zaahen is being added to PBE. 12h later, here I am with the finished video. Sorry if the quality and editing isn't at its best. Hope you like it anyway. xD

I was aiming for a couple of minutes and ended up with 7 minutes. Guess I just like hot edgy characters. :/

His voice sounds so familiar to Yone.  I couldn't find a confirmation on that though.

I was kinda expecting him to be a sup, so we would have the whole darkin team assembly. Aatrox top, Rhaast jungle, Naafiri mid, Zaahen sup, V*aa*rus adc :/

Hope you enjoy the video, I go get some sleep ;D
---------------------------------------
-------- Soundtrack --------
---------------------------------------
Shurima - Login Theme (From League of Legends Season 4)
---------------------------------------
---------- Timeline -----------
---------------------------------------
00:00 Xin Zhao
00:23 Yunara
00:49 Aatrox
01:34 Darkin
01:48 Rhaast & Kayn
02:15 Varus
02:45 Naafiri
03:12 Zoe
03:19 Sivir
03:32 Shuriman
03:40 Taunt
03:43 Azir
03:57 Nasus
04:09 Ascended
04:13 Renekton
04:24 1st Encounter
04:35 Kill
04:39 LeBlanc
04:50 Joke
04:58 Death
05:01 Respawn
05:24 Move