I received an e-mail about this yesterday. Very nice program and great for customers. It'll be interesting to find out how successful it is once the window closes in September and you can tally the trade in numbers.
Out of curiosity I checked the current MSRP of the 4B3 as it's been a long time since I have gotten any new gear and WOW, my oh my have the prices gone up nice I purchased my original 4B-SST and then shortly after the 4B-SST C-Series. I still have the C-Series powering my center channel.
I believe McIntosh has a similar program they have run from time to time over the years and that also seemed to be very popular.
If it proves successful and it possibly becomes a yearly event, like others mentioned it would be cool to see it include some of the other amps. I suspect the 7B would probably be the next most popular amp, that or perhaps the 3B?? Having all of the amps included of course would be great and if flexibility was there to not just upgrade like for like but to move to a different model, like a 4B to a 14B, or a 7B to a 28B, etc.