I think with all that is going on, it didn't make any sense to have a host GM in last night and realistically, in terms of kayfabe, who would take it?
That being said, I don't think there needed to be a GM last night. Bret Hart was attacked and that was probably for the best as it allowed the Nexus to get their contracts and allowed Vince to fir him basically. Also, Vince was there last night and there was announcement of a new GM. The fact of the matter is that if there was a guest host last night, he/she would have been completely over-shadowed by both the announcement og the GM and the appearance of Vince McMahon on Raw. Not to mention the fact that Raw really was pretty stacked last night and had a nice little over run. The guest host wouldn't have had any time to plug whatever they were plugging so I don't think it made any sense to have one in the first place.
I don't think that this is the end of the Guest Host scenario. I hear that Rob Zombie id due to host next week and that just show you that the WWE is happy with the Guest Host scenario. Right now would be a great time to end the Guest Host angle but I think they are going to keep with it. I mean, it would make sense to cancel it after last night but they are continuing on with it and that should be enough for a signal of intent on the part of the WWE.