Charlatan,
I think they are attempting to make it more "real world" if the world was actually set in the realm of Elder Scrolls. That is to say you have a group of people that love to adventure together - they form a guild.... but most of them are like me - I hate to craft (hate may be too strong of a word - I would just rather be off adventuring than standing at a forge). So this one person of the small guild - whom she dearly loves to fight with - needs an outlet as a crafter. This not only includes selling - but trading for materials, recipes, and all other things crafting so she joins The Tuatha Trade & Salvage Consortium where there are 200 other crafters she can converse with about "best possibles", trade with for supplies and recipes, make bargains, and then list her wares on the TT&SC market which supplies armor, weapons, etc to possibly 1000 member submarket of buyers.
With the ability to join 5 guilds you could be in 3 or 4 guilds just for the market. And yes, there may be some issues but no more than any other AH. I also see it as a way to keep down market prices - who is going to want to be a member of a trade guild that charges the highest prices (believe - it will get out which Trade Guild(s) to belong to - who has the best prices. Personally, I think it is quite clever and since Gaiscioch has always been a leader in new ideas - I think we have some crafters that can take off and run with this. New events even spring to mind - massive harvesting contests - crafting contests within this guild branch - Crafting and Marketing Leaders for this branch - we have a couple of great economists in our guild. Fog will always be the one true leader (gawd, starting to sound like a cult follower, but now we could have Elders just over this branch that were never Elders before. We need to look at this aspect of the game as a new challenge - and when has Gaiscioch not met it challenges head on - NEVER!
WE ARE GAISCIOCH!!!
And as far as the last part - there is still 8 months - give or take - for testing. Just keep checking your e-mail every day like I do for that invite. :)