While the new Tiamat would let Nasus get multiple Q procs, it also comes with downsides.
It delays CDR which costs him Q procs, it can't be bought early because he has to build tanky to lane, and it requires quite a lot of set up in lane so most players won't be able to make much use of it.
It also doesn't solve his real problems. He's still trivially easy to kite and has his only form of pseudo-CC gets doubly reduced by tenacity.
In the red posts it was noted it goes off of Attack Damage stat and not the total damage done. So the Q bonus damage is not splashed, only the Attack Damage value in the stats box. --- "Mud Turkey 13 is totally awesome!" - Your Mom