He is only human, but one would have hoped for a better reaction. The fans cheering him being substituted was very dickish, but the booing only really started after his reaction to it (i.e. walking off the field deliberately slowly whilst making provocative gestures at the crowd). It'll be a long way back for him from here.
In any event I think to some extent he is basically just copping the flack as a proxy for Emery and his team selections/tactics. My perception is that most of the fans, whilst thinking Xhaka is a bit crap, do not really harbour any great animosity towards him. Emery's popularity and support, however, are rapidly declining. Lots of clamour for Ljungberg to be put in charge for the remainder of the season, though I'm not really sure what is driving this, as there's not really any evidence of what he capable of.
Anyway, agree that the Xhaka business will likely be drawn out far longer than necessary, and this is bad for two reasons. One, because it will distract from the fact that once again Arsenal played really poorly, and let a 2 goal lead against ****ing Crystal Palace slip at home. Next two league games are Wolves and Leicester as well, so things could get real ugly real fast. And two, the fact that it has made Arsenal Fan TV relevant again, and that is never good.