Before people launch off into featureville (stereo, quad, kitchen sink, ect.), I think an 'exact' drop-in replacement for the 'original' Pokey would be a fantastic idea since the individual price has gone up to $20 a pop from BEST Electronics, and he limits you to one per order. And yes a stereo or quad version would also be a great addition, but I don't think it should come as a sacrifice to people who still need an original Pokey replacement. However if one device can can serve all instances so much the better.
Fred Quimby (batari), he of Harmony Cartridge and Harmony Encore Cartridge fame, showed a work-in-progress 40-pin DIP mounted ARM-based implementation of POKEY's sound generation capabilities called - fittingly enough - 'HOKEY." That was roughly 3 years ago. We have seen little about it in at least 2 years. This kind of thing, more than a "full" POKEY, is needed to keep the hobby viable - every HOKEY or equivalent in use for 7800 game cartridges will save a genuine POKEY for vintage A8 machines, 5200's and original Commando/Ballblazer cartridges and arcade machines. Such a limited sound-generator device would also help those who just want to make music - I mean, do all those stereo and quad-POKEY mods really need to run 2 or 4 separate keyboards, SIO interfaces and paddle sets? Of course not. One "full" POKEY and 3 HOKEY-like chips would give amazing audio possibilities without sacrificing vintage hardware.
Al has been cautiously optimistic about HOKEY in the few times it comes up in connection with 7800 homebrew carts - hopefully that means it might actually happen. If so, Fred could have a new customer base in A8 owners who want to do these advanced audio mods as well.