IMHO, there is a good chance that today's post-ban stuff will become pre-'04-ban, similar to what mattsd posted.
I am building up a stock of current post-ban receivers (ARs, FALs, etc.) and will be slowly building those up into rifles between now and '04.
I think that they will go after the firearms with pistol grip and mag insert outside of grip next. All receipts for ALL parts that go into the build up of these rifles will be saved and archived - in other words, document that your rifle is a full rifle prior to '04 with receipts, photos, etc. My guess is that possessing a bunch of pre-'04 lowers won't be worth squat - needs to be full rifle just like the '94 deal.
If for some crazy reason we don't see replacement legislation, or if there is a temporary lapse in AW ban, I would then already have the rifles, so I would only have to spend minimal dollars to quickly modify these rifles with collapsible stock, flash suppressor, and maybe bayo-lug post.
Also, keep increasing stock of mags.