I really like your deck and I wanted to put out some points:I do somewhat agree with merciless Executioner being a little too cute, I do find that 4 Lilianas is great, she is serviceable as a 2/3 lifelink and if you play a second you can sac it to flip either of them. She is great to leave back as a blcoker of 2 power creatures with lifelink negating some of the damage of bigger threats and when you attack she threatens to flip if they block. I don't like 4 Dromoka's Command in the main, it does nothing if you end up with no creatures(or at least is very limited), I would do a 2/2 split with Abzan Charm, because the meta is so diverse in threats that you want to diversify your answers.

Courser does seem to be the weakest link main deck adn I do like Grim Haruspex, because it dissuades from board wiping and can potentially unmorph for more Raptor returns. Rakshasa Deathdealer is the one more creature I believe you are missing main deck, it gives you some late game mana sink and gives you more 2 drops(since you don't have any 1 drops you want to at least put down a threat turn 2.

So I would -2 Dromoka's Command +2 Abzan Charm, -4 Courser of Kruphix -1 Fleecemane Lion(he dies to Languish even with Monstrosity so a split with Rakasha is good) +1 Liliana +3 Rakshasa Deathdealer. +1 Grim Haruspex.

Also in the side, you might want to reread Colossal Heroics, it costs 2 more for EACH creature after the first you target with it, so it costs 5 mana to give 2 creatures +2/+2. I really don't think there is a straight up good way to protect against Languish right now. You could side in 1 or 2 Grim Haruspex, that way you at least draw for all your creatures that die.

Just some thoughts I had.

That makes perfect sense. Courser of Kruphix is the weakest, I agree, and Rakshasa Deathdealer is something that I would be happy to get in a Collected Company despite being a 2-drop. Grim Haruspex I am still unsure about, but it would be a better fit as it can be retrieved by Collected Company, which Colossal Heroics can't. I'd definitively add it to the sideboard at least.

Was unaware of the Liliana, Heretical Healer  ^Flip legendary rule interaction. Being able to abuse the legendary rule actually helps a lot.

I like your current deck: +1

Any ideas for post-rotation changes? I am tempted to play Abzan CoCo after rotation, although I'm currently not willing to buy the playsets of Lili, Deathmist, and Den Protector ;).

And I have also another utility creature for you: Reclamation Sage. You could for instance substitute the Dromokas Command in your SB for them.

Post-rotation, I plan on at least replacing Athreos, God of Passage with Grim Haruspex, and Fleecemane Lion with Warden of the First Tree - assuming that the next release has literally nothing else worth playing. Pitiless Horde is also a significant possibility, as being able to put 10 additional damage on the battlefield at the end of the opponent's turn 4 is a great win condition. Honestly, other decks lose a LOT more than CoCo post-rotation. Abzan Rally needs Mogis's Marauder - CoCo doesn't.

Replaced 3 lands with 3 Elvish Mystic. Testing shows that this is an overall better choice due to Collected Company - despite the mana color inconvenience.