(long post ahead)
I don't like this idea because you shouldn't be able to tell if they're ignoring you for IC or OOC reasons. It's all IC, and you're free to ICly react to the snub, no matter whether it was deliberate or not.
I agree. The correlation between IC and OOC shouldn't be seen and since it is all IC, react appropriately IC'ly.
Show concern for the person who's spacing out because the character has been up since five in the morning. Or seems to have a lot on their mind. Consistently not getting sleep is unhealthy / can create problems and mistakes. Bring it up. (We show concern for or are critical of taller people who weigh 95 - 100 pounds, do the same for some who space out.) It's IC. So, rip into the character IC'ly. Or show concern where it's happening frequently (especially if it's happening in public - there are thieves about and people who enjoy fondling others ;) ) or smack them upside the head. Maybe outright ask them if they're not right in the head or did their mother drop them when they were a kid. There are a variety of things you can do IC'ly about this.
Now, sometimes people have an little emergency to handle [kid / dog / spills / lag / etc.] and that's understandable that you have to rush to handle it and can't go to the ooc lounge.
I understand where Myth is coming from and have been on both sides before. For the most part this isn't a problem in this game / community, but how about some RP manners and if busy in RL where it's going to take some time (work, cleaning, etc), don't log in and if tired, maybe going to fall asleep (if you catch yourself [I know a player who RP'd that wonderfully the next day when this happened]), log out in safe area? (Just a thought.)