Based upon what has happened in other countries, and extrapolating, my guesses are:
1. They'll continue to pick on small groups of firearms at a time ('assault weapons', 'Saturday Night Specials', etc.);
2. They'll tell you / us we have until a certain date to turn them in. After that it will be a misdemeanor or felony, with jail term. See
www.sksbuyback.org .
3. No door-to-door searches (at least at first), except for obvious cases, RKBA activists, etc.
4. Any reason to come to your home will be used as a pretext to search for firearms. Most LEO's will go along with this, IMHO.
5. In the background, they'll computerize the 4473's they don't already know about (via NICS, visits by BATF to FFL's, etc.). I don't see where this is all that tough. And, I'll bet some FFL's record serial numbers on these, even if they don't have to by law.
6. They'll begin having LEO's record and report serial numbers for firearms they find on motorists, etc.
7. Public relations campaigns will convert the public's perception of honest gunowners until we're seen as worse than drug dealers.
8. By the time they're done, most of the people with 'prohibited' firearms will have buried them in the ground, off of their own property.
And, so on. I sincerely believe that the logistical roadblocks to such an effort can be overcome by money, time, PR and ultimately, the fact that honest gunowners are inherently law-abiding.
I too don't understsnd the logic of getting rid of FFL-purchased firearms. If you ever bought a firearm on a 4473, I figure they'll just search your property in due course. Won't matter if you disposed of some or all of your firearms, IMHO. It wouldn't really surprise me if they went so far as to cross check records for membership in gun groups, CCW permits, maybe even gun-related books from folks like Amazon.Com, etc.
Paranoid? Well, I wouldn't bet my life on all of the above, but I don't find any of it beyond the pale. I think it is all feasible, in the long run. We're doing so well on fascism, I think technology could be artfully and efficiently used by these people to put the final nails in the RKBA coffin.
Regards from AZ