I agree with the rest, this topic is so vague and has so many what-ifs associated with it that it's probably not worth getting too worked up about. Failing to heed my own advice, here goes:
One of the biggest problems with the past AWB was the grandfathering issue - if a gun was made before a certain date, it was okay in its "evil" configuration, but if made after a certain date, it couldn't have certain "evil features." Some poor unsuspecting person not well versed in the law picks up a post-ban AR, for example, then sees a really cool stock at the gun show, slaps it on his AR, and BAM he has just committed a crime. There were also stories about people that had a post-ban rifle and a prohibited part confiscated during a search or raid, and by the time the weapon in question made it to the courtroom, the parts had mysteriously been assembled in such a way that the weapon violated the law.
Apart from the sheer stupidity and unconstitutionality of the appearance-based AWB, it endangered poor unsuspecting novice firearms owners, it endangered firearms enthusiasts that owned a combination of pre- and post-ban weapons and parts, and it was very difficult to enforce as well as being completely impractical in reducing crime. It also drove up prices AND sales of pre- and post-ban rifles as well as parts.
- the anti-gunners, the hard core ones, learned a lot from the previous assault weapons ban - the cosmetic features were easy enough to modify, leading to non-collapsing collapsible stocks, bayonet lugs being ground off to prevent drive-by bayonettings, and those dumb-looking thumbhole stocks. What did we learn from this? If you want to ban a gun, LIST it by NAME - you can bet that when the next assault weapons ban comes out, it will just say something like "All variants and models of the AK-47 series rifle" or something like that.
Alternately, the ban will encompass a much broader field of weapons, such as all magazine-fed semi-automatics or something similar to that.
I also believe that the next one will not be a "ban" which has an expiration date, but a law, which does not expire. Finally, any future assault weapons legislation will not have a grandfather clause - after a certain date, possession is a felony, assembled or not.
The likelihood of any assault-weapons law passing is something you will have to decide for yourself based on your opinions of our esteemed representatives on Capitol Hill, but anti-gunners and pro-gunners both learned from the last one, and you can bet it will be different.