Good questions:
Why wouldn’t an affiliate do this for themselves, create their own site and post articles to it.
I would think working in a group would help keep you more motivated, and they would get some guidance from a mentor type to start. I think the hardest part of doing anything, is getting started, for me anyway.
How would you keep affiliates motivated to keep doing this, when initially they aren’t making money.
This one is the hardest part, it is extremely hard to find someone with a passion for just promoting casinos without the income 
again I think a group working together would help a bit on this, but you’re right for 99% of people that will not be enough. I may have to throw in other small incentives until they start earning on there own.
What happens when an affiliate no longer writes or is unreliable.
I was thinking a 3 page a week minimum, and if they are gone for more then a few months they would be replaced. I was also thinking the most active affiliates would get a prime link spot on the main page.
How do you make someone believe that you won’t “run away” with the domain.
This one is also hard, but that is also why each affiliate will have there own affiliate account, so if anything did happen they would keep any players tagged to them for life.
As most affiliates have more then one site, I think this would get them started, and once they start making money I’m sure most would branch out and start there own site.
Im really looking for some fresh ideas, I have been doing this since 09 and make about 5k a month right now. At one point I was making around 13k a month, and I want to get back to that. The problem I have is, I am getting bored with it and need to spice it up a bit. I think working with others might help with that.