I'll start with the post I quoted:
https://forum.paradoxplaza.com/foru...-the-2-5-2-patch.908792/page-17#post-20687735
The reasons are pretty obvious. They existed because they were realistic, but also to make blobbing harder. They were cut because people complained they made the game too hard (which they didn't if you weren't trash at the game).
So, in short, bring back:
-The modifier that increases likelihood of vassal to seek independence the further it is from the capital of the realm
Hmm maybe that could be done. If it isn't already, I mean, there are so many behind-the-scenes maintenance events in CK2Plus I don't know if e.g. Independece faction don't already account for distance ^^
-Pre-SoA vassal-on-vassal plots if CA is below high
Why only when CA was below high? Plots don't seem to be something a top liege could forbid, with them being secret and all.
However, plots between vassals sound good. What did they use to do that isn't currently in?
-Mercs having a chance (IIRC 50%) of revolting if unpaid, instead of just disbanding
That isn't in anymore? Ok that one I upvote, that should be a thing.
-Pre-RoI vassal revolts with each tag being independent with their diplomacy, alliances and full levies
I don't know about this one. I feel like revolts are strong enough at the moment, no need to give them more power.
I also feel that since factions are more logical in CK2Plus, vassals tend to organize better within the realm, even without help from outside. Add 3 king allies to a revolt where 90% of your vassals rebell would be overkill imo.
-Counter-assassination event on discovered successful or failed assassination of you or IIRC your close family
Assasinations were removed, right? The post you quoted before stated that, so I don't see why we need counter-assasinations.
Your failed attempts already give an hefty opinion malus to your victim and his family, so they are likely to seek revenge on you later. I think seeking revenge even is an ambition iirc.
Direct counter-assasinations don't make sense imo. It's not like the (surviving) victim is going to say "hey assasin, so you failed to kill me. Care to kill the guy that told you to do so for the same amount?"
-Assembly voting by all de jure vassals
I honestly don't remember this. What did it use to do?
Curiously CK2Plus has kept one of the features that was cut in vanilla IMO for a good reason - the numerous ambitions. The huge array of ambitions serve only as a micro-intensive min-max mini-game that's many times worse in CK2Plus.
Well, I have to disagree with you here: Tastes differ, and I for one find the vanilla ambitions to be hilariousely lacking.
Ambitions are there to set mini-goals for characters and thus for roleplaying as well as giving an idea what a chracter "is up to". In vanilla that rotates between "gain a title" and "become councillor" or so, which feels more EU4 to me than CK2.
Thus personally I am very happy that CK2Plus offers many ambitions.
Overall, I don't think the mod is "casual" in any way currently. Most of the things you mentioned were not simply cut from the game, but replaced with something else in the wake of a mechanic rework. And blobbing has always been easy in vanilla CK2.
And this mod here especially added many more mechanics and tweaks that make blobbing very hard. You have a few good points there, but what I think is feasible of them wouldn't have that much of an impact on gameplay imo.