I don't think too many people would be opposed to using a PIC chip. As long as the supporting circuitry is designed correctly, there's no reason to think it shouldn't last a long, long time. That being said, it would also be cool if the programming of the chip was available for download, or at least keep a pile of them around pre-burned so if someone's does go belly up, getting it going again isn't impossible. (Might be worth making the chip socketed)
There are some PCB houses that will make up the whole board for you and it's generally pretty cost effective. Beats soldering oodles of these things together in your spare time. Conversely, you could just sell it as a kit with a board and a bag of parts for those of us that can solder on our own. My guess is, you'd find a pretty ready market for the DIY approach.
I'd take a day to solder one of those up. What a great way to get some of my display phones operable without much hassle or a fat wad of 25pr running back to the phone closet. I could screw that to the back of the cabinet and just plug the phones in directly. Then its just a couple pairs to hitch up to the pbx.
