I'm not saying nobody should make sprites like Beefmo's, I think they're lovely. Nor am I even advocating a non-isometric sprite system. I am
defending such a system, since several people have criticized the fact that most artists have submitted non-isometric sprites, but I'm also arguing that you can still use an isometric system without looking to Super Mario RPG and Tactics Ogre idling stances for your isometric poses, which I submit is a bad idea no matter what angle you prefer to look at your sprites from. I don't wish to insult Jadael and Xandrin here, mind -- I truly adore Jadael's 3D dwarves based on the Super Mario RPG style (I'm just very strongly arguing that this style is inappropriate for actual use), and Xandrin was suggesting Tactics Ogre with the idea of having multiple facings and walk animations, not with the intent of just using a single facing's idle frame to represent the entire unit.
I think I should clarify my use of the word iconic, since I apparently gave the impression that I meant it as a synonym for 2D. I'm actually saying that both 2D and isometric sprites should have an iconic quality. They should be memorable and symbolic, interesting and representative. Deon's mayor, for example, has an upturned hand, and a large mouth, as if she's speaking and gesturing. Those are what I mean by iconic elements in pose and expression.
They should not imply a specificity that does not exist.
This is a great-sounding principle but it falls flat pretty fast when you examine it. Does DF specify the style of the breastplates, the height of the grass, the texture of a wall, or the length of a sword? No. Does that mean that artists shouldn't depict these things for fear of making an invalid implication? Of course not. The point of a visualizer is not only to depict the details that DF does contain, but fill in the details on which it's silent.
Taken literally and to an absurd extreme, you're certainly right, but you are misinterpreting my point by a fair distance when taking it that far. Aligning all your dwarves to have a southeast facing is not just adding details -- it is like making every workshop in your visualizer look like it's made out of microcline and justifying it by saying you don't know what material the workshop is really made out of. If you don't know what material it's made out of, sketch in the details and use a generic gray rock without specifying with such precision as to jar the viewer with the degree of its inaccuracy. If you don't have sprites for every type of tree, better to make your generic tree sprite look like an oak than a willow. I know my dwarf travelling to the north is not facing to the east -- so why is your sprite so overwhelmingly dead set on convincing me otherwise? The purpose of a visualizer is not to contradict what I already know about my fortress, and it should avoid doing so.
As I said in the post you are quoting, there's a big difference between having a character look into the right and aligning everything's head, shoulders, chest, hips, and feet in the same way on the same axis. One is artistic expression to provide interest and detail to the sprite -- the other uses a bad design principle that will tend to strip away the iconic quality and encourage a literal interpretation of facing, giving a false and disjointed feel to your fortress. Following this guideline and having isometric sprites are not mutually exclusive.