I think any market place site will only ever be as good as the content it has on offer, Tranq and if other grids find they have to compete then I would expect the quality to improve with some grids having cherished brands and merchants specializing in order to attract residents and travelers. I have always felt in-world trade suffers because of web based markets and I'm sure that has contributed to the decline in Second Life but they exist and more will open (Aviworlds is saying they will open one). I think commercial grids will have to look to other ways to monetize. Land hosting will remain the greatest source of income I'm sure but more and more small grids serving role play and other entertainment venues will increase and likely they will have in-world stores specializing in themed clothing, props and vehicles much like happens in Second Life.
I am not sure yet exactly how the export perms are going to work out but my own plan is to not allow export of my specialized items like combat hud and weapons for example to leave my world. I want them to be available to role players who visit my world but I am quite happy for hypergrid visitors to bring their own clothes and inventory they bought elsewhere with them. I might say the same for adult rated sims who will probably want to specialize too. In deed, I see the future of the Metaverse as many small worlds with a particular theme or entertainment and a lot of RPG's just as it happened in Second Life with many regions specializing. With hypergrid and an open market everything that worked for Second Life can work for the free Metaverse and a damn sight cheaper!