FFXI is built on the PS2's dev environment, a major reason they are moving away from continuing updates on it and to just maintenance/QoL changes only after this month's conclusion. It's also built on an engine that was originally designed for single player console games.

Bringing together the technologies is not feasible. They've mentioned in a Q&A that even if FFXI was still as popular at its peak, even though they would have the money to justify continuing it, the dev environment would still be a problem.