The biggest issue is that it's something like a 1:4:10 Tank:HealerPS population ratio. The Data Centers themselves are already Duty Finder merged between their worlds(ie Chaos Center plays with anyone else on that Center). The Data Centers themselves are located in different places as attempts to reduce lag for players of those regions, among other reasons.

For this to work it'd be easier if there was only one Data Center, like back in the 1.0 days, but we have 2(soon to be 3 with EU getting theirs sometime before 4.0). Since there are multiple Data Centers, they'd have to choose a 'Host' Center, which would end up lagging players NOT from that Center.