I'm aware that they've claimed that multiple times; however, it certainly would not be impossible to do. It may take a little effort(apparently more than they're willing to exert) but its completely possible. (There's a post somewhere where the community coordinator stated it was possible but would require a revamp).
You'd think that in the process of designing the game it would've crossed their minds to implement a cross-server system, but it is fan made so its understandable.
Profits aside, it would be really nice to eventually see this just to allow people to play the game without waiting up to 20-40 minutes at times.
If red world was extended to another server, would it actually be a negative impact to the economy? It's just an extension to the amount of total players playing the server at a time. Rarity and difficulty wouldn't be changed just because the amount of players for a world type(red/blue) is scaled up, that doesn't mean a pokemon/item/etc would become less rare.
Imagine there was Red 1 and Red 2, Blue 1 and Blue 2 where red and blue were different saved, 1 and 2 are extensions to the saves allowing for more players to play each red/blue server.