Huh, never realized how simple the schematic really was on the WPC-89 boards. Once you empty the real estate by moving to SMT, it starts to look downright elegant in comparison to the originals. Nice clean layout, well done! Does it still include a real-time-clock? Not sure what WPC-89 games had clock based features.
To answer the other questions that came up.....
As a hobby, we have to get used to surface mount components, thru-hole stuff is being discontinued left and right by every major supplier. We're hitting the point that duplicating old designs with thru-hole parts is simply not viable any longer. As a hobby we must adapt as there's no other option. I can't remember the last time at work that we brought in a new design for a customer that had a thru-hole IC other than opto isolators. NOBODY is designing new thru-hole product in any quantity. Too big, cost too much, costlier to manufacture, and harder to design boards with thru-hole IC's. Once you get used to it, even repair work is often easier and quicker with SMT parts than thru-hole. Just takes some practice.
Seriously, the semiconductor market right now is absolutely bonkers. We're getting notifications on a daily basis of huge lead times, parts being discontinued, last time buy notices, you name it. Atmega processors are a two year lead time right now and still extending. PIC's aren't far behind. Hell, I just got a 4 month lead time for molex crimps.
The power supply idea is well proven via existing daughter-board kits. This design integrates it into the CPU board as opposed to having it as a separate module. There's no concern at all. Good solution to drastically reducing reset issues.
Sound boards for many designs are impossible to make exact duplicates to the originals. The original DAC chips are long obsolete and not available in any reliable quantity, and audio amp chips are also disappearing in rapid succession. One customer at work is on their third major redesign because of audio amps being discontinued.