For X@COM I went with units represented by triangles (no longer pure ASCII, obviously), but this wouldn't really work for your most RL's because you need much greater variety in terms of representation (different symbols), whereas X-COM has little enough variety that color is usually sufficient to differentiate unit types.
Heroic Fisticuffs' GnomeSquad has an interesting method of showing facing using any character/symbol you want by showing a translucent blue over the adjacent cell towards which they're facing. Not aesthetically pleasing, but it gets the job done.
Using FOV shading sounds like a pretty effective way to solve the problem, and it could work pretty well if you've got unlimited colors to work with, though maybe not so well if you have a huge number of units in an area at any given time. It does, however, look pretty neat if you faintly highlight all entity FOVs and allow overlapping FOVs to strengthen the color based on the number of FOVs overlapping in each cell. (I've tried it: The X@COM demo does this when you have the option turned on.)
I think AI issues are mostly negligible, since you can easily integrate turning costs into the pathfinding routines, and make turning a prerequisite for doing actions that require a direction.
Gameplay is another issue entirely. To go the facing route I'd say it definitely has to be a primary feature. (For example, it is a central feature for a pure stealth/thief game I've thought about making--makes sneaking around so much more fun
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