As far as I am concerned, I would not mind to pay for modules that I find useful, or to be payed for modules that I write. But I see at least 2 problems:
1. Much of the "spirit" of the PI forum is based on the "pro bono" work of volunteers. This spirit can quickly evaporate if PI becomes too commercial. (Niall, just imagine you would want to charge for the work you are doing here...)
2. I dont see that anyone can earn more than some pocket money from this. Considering the number of average hits that an article in this forum has, PI probably has 40-100 active users. Assume 20% are buying a module for $10, you would earn $80-$200. At typical daily rates between $200-$800 per day in the software industry, that would at most pay for 1 day of work...
AFAIK, I would rather prefer to continue in the mode that I did in the past, without having to go through the complications of going commercial (which also has implications regarding tax and liability). I would continue writing modules that I find interesting, distribute them for free. For this, I provide no guarantees, and the level of documentation/quality/support that I find adequate or am able to provide. And I am paid by the fun, mainly...
Just my 2 cents,
Georg