I'm sure you've considered these angels already but what about Linvala, Keeper of Silence & Platinum Angel?

Another demon you could perhaps try out would be Rakdos, Lord of Riots - Cheat him out with Kaalia or the amulet and then you may be able to drop more scary bastards for cheap.

Lastly, a couple more dragons to consider might be Scourge of Kher Ridges (seeing as most of your creatures fly, potentially a 1-sided wipe for you with the first ability which can annoyingly be repeated) & Skithiryx, the Blight Dragon just because he's a badass (also pumpable with Moonveil for an added janky infect win-con).

Another new card that you should probably find a home for in here: Break Through the Line

I reckon that could solve a few of Kaalia's problems.

Ugh, Break Through the Line + Master of Cruelties . I suddenly regret the suggestion. In fact, I demand that you remove both cards from this deck right now.

Also, Break Through the Line + Blinding Angel. Stahp.

Thanks for all the suggestions Forkbeard! Break Through the Line has been a fantastic addition and I've been using for a couple months now. Break Through the Line + Master of Cruelties is prettaaaaay terrible for my opponents. Poor them. Not sure if I've killed you with this combo yet. It'll happen, just give it time.

I'll pass on Skittles, just because I'd prefer to have creatures with more immediate impact and generally am not looking to use infect to win in this deck. I feel like he's a "good stuff" addition in any black deck and I'm trying for a little more focus with the angels, demons and dragons here.

Rakdos, Lord of Riots I'm less inclined to play. I'm not sure how reliably I'll be able to make an opponent lose life each turn and again, I think I'd prefer creatures with more immediate impact to play.

All of the other things you've pointed out though - yes. I'll be seeking them out and trying to find room for them in here. But what to cut, that's the tough decision...