Hey Argyle! Glad to see you posting in this forum

I don't see why either should be eliminated in the long run, as neither is in competition with the other's niche.
They will likely survive a long time, like coke and pepsi, or McDonalds and Taco Bell. It's all a matter of taste 
It's also very likely that in the long run none of the two forums will survive. One of the few things that I learned in my entrepreneurship classes is that pioneers usually get shot. And the more the product is a complex one, the more the above is true. Yes, Coke, Pepsi, McDonalds and Taco seem to be an exception to this rule, but that's because their core products are very simple. When the core product is simple, then it's all about marketing, catering, operations management, etc.
But when the core product is a complex one (such as the product of an internet forum) and it is a brand new product (such as the product of WWGHA or IGI), it evolves so quickly, that very often even the organization that invented it can't keep up to the standards set by the development of this product. And very often an emerging organization turns out to be more prepared for the new requirements.
Let me give you an example: The first graphical computer operating system was developed by Xerox, then it was bought and developed further by Apple, then it was stolen and developed further by Microsoft. That's how we have Windows now. Currently, all the three companies exist and are successful companies, but only one of them dominates the market of desktop and laptop computer operating systems, and that's the last-in company – Microsoft.
For a moment I imagine that I am a pirate like Bill Gates and I see a lot that could be stolen from WWGHA and very little to steal from IGI.
I hope it doesn't sound too cocky to you, but the only reason why IGI still has a niche, is because WWGHA leaves a niche. Now it's easy – WWGHA are the bad guys and IGI are the good guys – plain and simple. But that's because WWGHA is not bad enough yet. When it (or another forum of this kind) becomes really bad – I mean overwhelmingly bad, so bad that there is no proportional level of good to counter with, then IGI will simply become redundant.
You probably wonder what I mean with “overwhelmingly bad”. I guess you've heard Gloria Steinem's thought: “The truth will set you free, but first it will piss you off.” Well, my impression is that IGI is full of theists who simply can't or don't want to overcome the piss-off stage, so their choice is the IGI light motive – to goof around and try to affirm their religious positions. When WWGHA becomes “overwhelmingly bad” theists will have no other choice but try to overcome the piss-off stage.