Probably the last big American OO layout with outside third rail was the Saint Anne of Ed Costello, featured in RMC in 1979 (more here). In the cover photo of the issue the third rail is just barely visible in the lower right corner. As is noted in that article, early insulated wheelsets had a tendency to fall apart (ever see any Famoco trucks?) and three rail eliminated that issue, the wheels were all on solidly.
I recall maybe ten years ago a collector contacted me, they had a large outside third rail OO layout in storage. Maybe someone will get one set up and running again, but I am feeling pretty doubtful to be honest. Wheels falling apart are not an issue now, and installing a third rail is yet one more complication toward working in an already difficult modeling gauge. Although who knows, if I build another layout I might lay a test track with outside third rail.
For now though, I will just enjoy looking at it as it is, the only outside 3rd rail model to ever land on my workbench.