Ragg, it still isn't feasible to calculate everyone's threat. In order to do so you'd need to:
1) know the names and ranks of all spells cast by everyone,
2) know the amount of damage/healing done by spells cast by everyone,
3) know what talents everyone had,
4) know what items everyone had equipped,
5) know what everyone was targetting,
6) know what everyone's target was targetting,
7) know what buffs and debuffs everyone had,
8) know what buffs and debuffs everyone's target had,
9) know what stance or form everyone was in,
10) and probably some other stuff.
1 and 2 have an obvious issue -- if someone is too far away, you can't see what they're casting. If you have multiple people in your raid running Assessment, compare numbers after a fight. I'll bet you they're not exactly the same, especially if it's a large-area fight like Gruul, Void Reaver, Supremus, or Archimonde.
3 and 4 also suffer from range restrictions. If someone across the room swaps items or assigns a stray talent point, you won't know. In order to keep even somewhat accurate track of everyone's equipped items and talents, you'd have to be constantly inspecting people.
5, 6, 7, and 8 are possible.
9 is possible for priests (shadowform is a buff) and druids (forms are buffs) but as far as I know it's not possible to detect what stance a warrior is in, which is a big problem since your tank is usually a warrior and there's quite a difference between the threat generated by a warrior performing the same actions in the same gear with the same talents depending on what stance he is in.
If you look through the Threat-1.0 code, you'll see that more complicated things are tracked for some classes, like matching Lightning Overload procs to specific spellcasts (since LO procs look like a second cast of the same spell but cause no threat).
Another issue is that it's not currently possible to tell when many debuffs are refreshed if the first cast wasn't yours.
2.4 may change some of these, but certainly won't solve the range issues, or the warrior stance detection issue. Even if it were possible to do all of these things, it would be an enormous waste of CPU cycles when it's much simpler and more efficient just to ask each person to calculate and broadcast their own threat. :P
Well, it would chiefly be useful for DPS classes who want to know what kinda threat a tank without a threat meter installed is putting out, in which case range wouldn't be an issue, since if you're DPSing the boss you're probably within 50 yards of the tank at the most. I guess the stance thing is the big roadblock here, although I suppose you could assume they're in Defensive Stance. Is there a way to detect stance changes at all?
As far as I know, no, there is no way to detect stance changes. Even if there were, it wouldn't help you if the warrior was already in a stance when you arrived and never changed stances. Basically, although you could guess at the threat generated by a tank (or anyone else), you'd never be as accurate as a synced system that only calculated your own threat and received others' self-calulated threat values, which in turn is less accurate than the actual Blizzard system which is intentionally hidden. And really, the only fights where it's critical to stay at a certain position on the threat list (Gruul, Void Reaver, Gurtogg Bloodboil) rather than just "don't take aggro from the single tank" are in 25-mans where your tank probably has a threat calculation engine installed anyway. And it would still consume ridiculous amounts of CPU cycles to perform all those calculations, when it'd be much cheaper and not significantly less accurate just to pay attention to your damage output compared to the tank's damage output.
I don't think it's a limitation of the core, more a lack of code written to manipulate the data in that way. I've managed to get a very limited display of damage done to certain targets, using a copy of the Damage Taken set that shows non-group members, but it only shows ability totals (i.e. all damage taken from fireballs), not a breakdown by person (i.e. damage taken from MageA's fireballs vs damage taken from MageB's fireballs), but as it was too limited to be of much use, I'm no longer using it, so I don't have the exact settings.
You can create multiple windows, but as far as I know there's no way to launch a new window from an existing window. Could be a nice feature though... shift-click on someone in the Damage Dealt list to open a new window showing the details, for example. I've haven't used Recount extensively; what does the "split windows" feature do?
Currently, I don't think there's a way to dynamically control what the other window is showing. Recount, for example, will allow you to see your damage spread (damage dealt details), mousing over will show you the hit details (damage dealt hit details) on the 2nd half of the window. This allows you to see things rapidly and with a pretty gui. [The feature you mention actually already exists].
So currently, say you shift click yourself to show the details, there's no way to 'only' provide that new window with a different key, you'd have to manually right click on that new window and click on the new item, or simply to close and re shift click another. Recount makes this much easier where you won't get a tendinitis from clicking so much. In a sense, assessment is pretty powerful in having multiple instances of assessments out (besides the fact that new windows need to be reconfigured every time), but weaker in relating those windows together; a sort of sacrifice that is needed to preserve a very dynamic module.
But for my own personal need, I don't need a million assessment meters, and the only reason I use assessment over recount is simply because it's more customizable with possibilities that are pretty strong in practically creating a meter for everything. I would be very happy with shift clicking opening a single window and every other shift click will interact with the same window as opposed to opening a new one, and that window to be split so you can access further down without clicking much.
I really prefer Assessment's presentation to Recount with one big glaring exception... Not being able to merge/unmerge pets retroactively is extremely annoying. Violation and Recount can both do it, why not add that to Assessment (I assume that means running the collection with "merge off" and then allowing a merge in the "presentation layer"). Anyway it is a very important feature in my view.
Anyone happen to know if it'll not be too long before a 2.4 compatible version is available? Not pushing, just curious. If it's going to be a while (i.e. a few weeks) I'll probably grab Recount at least to tide over. (I don't really need the extra whizbang Recount offers, so it's likely I'll switch back when it's ready. Curiosity killed the cat, but satisfaction brought him back & all that. Not having them would drive me a little nuts I think.)