It's essentially the same system as allowing PS2(3)/360/PC users to play on the same FFXI servers so they could do it if they want, there's just realistically no reason to have a cross-server economy.
@Player pool:
If no one creates say a steel celata, no one will suddenly create it just because people across the servers can buy it. If an item isn't supplied ever it won't suddenly be supplied. While true you can have more buyers in a sense, you won't automatically want to make something you've never wanted to before.
