Hmmmm, I think it is difficult to generalize. There are bags which seem to remain it bags for long time, such as the Balenciaga. Maybe because it simply IS great design AND a very practical bag. I don't think I will ever get tired of that.
However a bag like the Paddington you mentioned is getting less popular (at least where I live), maybe because it is not very practical with the heavy padlock.
At the moment I don't feel there is any new bag, everybody around me (incl. myself) is dying to get. There is a slight interest in the Darel Charlotte bag, but, you don't see any of the it girls wearing it here in my area. In my opinion the design isn't significant enough.
Maybe there are simply so many gorgeous bags on the market, that there won't be a specific one dominating? Or because people simply have got enough of hunting and fighting for the same bag?