Having spent a ton of time in PI and a fair amount of time downtown both in Church St. Station's final days and today, there's a fundamental flaw in these arguments. The current crowds downtown and the potential target audience for a Disney nightlife experience are completely different.
PI was conceived in the 1980s, when Orlando and the tourism industry were fundamentally different. Most guests drove here, and most of the rest rented a car. There were limited hotels on property, a lot of the land west of WDW was orange groves, so the major "hub" for tourist hotels was still northern I-Drive (a good 15 minutes closer to downtown than WDW). And Orlando was still a small Southern city. It was the perfect storm to allow CSC to thrive.
Flash-forward to 2012. Thanks to Magic Express, fewer people drive. And many that do stay in the newer hotels/developments west of DTD; Orange Lake, for example, is at least 20 to 25 minutes further away from downtown than I-Drive. Traffic is more of a bear, too, because the city of Orlando has exploded with growth.
At the same time, the "real" Orlando has fundamentally changed. When CSC opened, Deltona was still a retirement community and Heathrow didn't exist--CSC relied on tourists because it had no other customer base. Since then, many new companies have opened in Orange and Seminole counties, even corporate headquarters. At the same time, UCF went from another regional commuter school to the largest university in Florida. There are a lot more (young) locals within a half hour of downtown than there were in 1987. Downtown caters to them now, not tourists.
Most of the kids downtown these days never went to PI--partly because it was too much hassle, but mostly because they weren't 21 as of September 2008. If even 5% of the typical Friday night crowd on Orange Avenue were not locals, I would be shocked.
At the same time, the need for nightlife for tourists hasn't disappeared, we just need to realize it would have to be a more centralized location than CSC was. But bringing downtown into a discussion of PI is like discussing pay phones at Art of Animation.