This post is pretty long, sorry there's a lot of content to cover Verdant_Squire, so i've condensed it in spoiler's regarding the original sourced question and posted the replies. Toady's the only real official authority on your questions though bear mind.
1. Will creatures always necessarily hold grudges against their former partners, or is it possible for a relationship to simply "not work out" with no ill-will between either person involved? What causes someone to end a relationship, aside from unwillingness to commit?
I don't remember the mechanics of Toady discussing this, so im not sure where you got that data rather than a educated guess. There will be more relationship types (war-buddies, scholar buddies) and divorces in the new release (offsite re-marriage too) but im not sure on the precise detail (any links or quotes would help)
2b. As an extension of the previous question, how will already existing claims interact with the new villain system? Would current position holders be able to recognize potential claimants as a threat, and dispose of them via assassins?
Or identify a artifact that either belongs to them through a link, Toady can answer more fluently but i thought id just tag onto this question to explain that it would probaly be feasible if proper artifact claims were put in since title-related pre-aquisition of artifacts isnt in at the moment, rather than the personal links dwarves have with a artifact dedicated to a holy man, certain place, or family ancestor/lineage to act on.
2c. Will we see the children of ruling monarchs engage in the historically time honored tradition of sibling rivarly over who gets to be the heir? Would the degree to which this occurs be affected by how much the civ in question values family / power?
See my above reply, you probably won't see squabbling over the position until the law & property Arc (in devgoals) , right now the only gravitation suggested to us (or to dwarves) is that villians move towards positions based on their desires individually or towards artifacts (again to prior point that requiring a certain nominated artifact to rule/show royal authority and legitimacy wasn't implemented yet)
3. Will villains attempt to place people other than themselves in civ ruler positions? For example, could a demon or rival civ leader try to position a more easily influenced or cowardly character as the leader of a neighboring civ? If so, is it necessary for said character to already be caught up in the web, or could this happen without their knowledge of the strings being pulled?
This features in the most relevant development story, though if you understand that sometimes its easier to just remove difficult actors and easily convert softer targets, unlike Chief Cup-Bearer Shorast (corrupted 95 - d.97) who got splatted shortly after by a cyclops in december's devlog. Im not sure what extent, they would control people through the network or for what purpose as we'll have to see what Toady does regarding outside influences changing behaviour of people in the web presently.
Id be a bit dissapointed to not expect outside forces to try and meddle with our present civilization of dwarves by proxy but dwarven civilizations are well guarded and lawful, if exploitably greedy.
4. What happens if a coup attempt doesn't quite go the way the plotters were hoping?
Refer to what the civilization has in treason crime ethics and have the hammerer (executioner) on speed dial if nessecary.
5. What exactly happens if the monarch of a civ is the primary propagator of a villain network? Would there basically be no consequences whatsoever to be uncovered in that situation? [Who the heck is gonna punish you when you're already at the top of the chain?]
Normally refer to what the entity ethics and position tokens will allow with [PUNISHMENT_EXEMPT], Toady might put in a overriding workaround (or not), like deposing and incarcerating the king, finding a new monarch then trialling and putting to the hammerer the old monarch at the injunction of doing criminal activities against the current or at expense how vunerable they are stripped of title.
6. Does the abstracted "personal account" manifest in the world in any way, even if said manifestations are entirely arbitrary? IE: The hearthpeople of a rich lord being better equipped in general?
Nobody's rushing too fast to re-impliment economy, it'll exist from Toady's comments but not in a tangible way in fortress mode, rarely being demonstrated usually.
At the moment, armor and quality sorting is done by [PRECEDENCE] position value which is why the general's troops from off-map always arrive with the best skills and if they were in uniform, nice probably steel gear, and why siegers (being 190 precedence captains as a single type of core unit) are all kind of crummy in equipment in copper and sometimes iron. Generals are 50 precedence, and hence everyone travelling with them in squad share the benefit. Precedence 1 monarchs also tend to wear masterwork clothes in adventuremode.
Nobody's been fighting real actual trained troops for years unless a fresh recruit gains experience through partaking battles naturally (somehow surviving). There's no way to change this without damaging balance as captains are hardcoded and can't be duplicated for 'ranks' of soldiers varying in equipment and ability.
- A fun tip is that all people present on the lists for assigning furniture are actually assigned per the precedence that they presently rank, so you can muncipally see everyone who's important near the top of the list.