So just like Koltira and Thassarian, just instead of homosexual Lifepartner they would be probably just slightly homo lifepartners.
First, Tirion as a Paladin is already boring as shit and turning him into a Death Knight takes everything away that defined his character without really adding something.
Saidan would have at least the potential to be awesome in his rage and vengeance against Balnazzar.
Renault could have been a really interesting Character as Hoursemen. First, he could try to redeem himself in Undeath, he could make things clear with his brother again and he would also have some connection to Balnazzar and be fucking pissed at him. After all, nearly everything that went miserable in his life was because of Balnazzar.
Tirion on the other Hand...yeah, what could he add to the Ebon Blade? We all know, a faction conflict between Paladins and Death Knights would be really really awesome, that's why there will probably no consequences for the invading of Light's Hope and the Paladins will eat it.