I think this thread is old but I've been think on this subject for a while now and have some thoughts
I think Cultivation did indeed kill honor, maybe for his own sake or a compulsion from her shard, let me explain
I assume honor allowed odium onto roshar cause well refugees honors not gonna say no is he or even could he . Then Odium did something singed followed Odium, men switched to Honor, Honor then swore to defeat/imprison odium or perhaps to protect ,mankind/ the cosmere from Odium or some variant on this likely the oath pact is involved in some way.
Point being that as a god of oaths honor is now locked in this battle with odium endlessly, one he can't win . So after thousands of years of conflict with no end, honor knows he should relent in some way as this would be better for his people but cant due to his oaths. I think this causes his madness which eventually leads to cultivation helping to shatter him so she doesn't have to see him suffer.
Alternative or maybe in addition to, let consider cultivation position in all this. Odium and honor war for thousands of years, this satisfied both of their shards intents but not cultivation, she wants to see things grow and change but considering how repetitive life on roshar had become during the countless desolation with knowledge being reset again and again, entire cultures fading away and new one starting just to be wiped away. Rinse n Repeat.
Perhaps cultivation was force by her shards intent to make things actually change and the only way to do this was to destroy one of the two. We can assume that honor + cultivation couldn't directly oppose odium either due to agreements or simple strength else they'd of dealt with him at the start of this mess. So Cultivation desperate to see the world change again, in any way and having watch Honor descend into madness decided to team with odium to splinter honor.
This would also explain why she now hate/dislikes mankind, honor let me him, honor defend them and that led to his madness and death. Easier to blame mankind, Spren n Bonds for Honors end than herself.
She defiantly has a master plan and has perhaps touched more people, Ziel for one, she offered nightblood to Dalinar i think which mean she got its from Ziel at some stage (maybe in trade for granting him access to life light to sustain his being instead of breaths) and gave it to Nahal i assume at some stage.
I also kind of believe in Cultivation had been planning to replace all of roshar Shard vessels with new hosts. Tarvangian , Dalinar and lift, were all touched by her not the night watchers.
She's killed odium as revenge for honor and replacement him with someone shes think will control the power better, she set up Dalinar to perhaps reconnect the splinters of honor and Lift might just be being groomed to succeed cultivation herself because I don't think Cultivation wants to live anymore, after getting her revenge she might be seeking her own end as atonement for her part in honors end.
She got a lot going on and to be honest I'm terrified of her, people and shard shake when they talk of odium but odium's fight were direct(ish) conflicts that left him hurt or weakened from them. Where as Cultivation has now directly splintered one Shard, Killed and replaced a different Vessel and might be trying to restore a splintered shard. Woman is terrifying and i just hope she on our side.