I of the opinion that unified servers are needed but it required for the Global to have any chance of surviving for meaningful amount of time. Reason I say this is player count on Global over past year are more or less not great.
On Steam it tracks active player in game and at Steam launch in August it was around 20k active in game, as of right now it barely holds 4k active players, that almost 80% drop off. Now granted this does not include Xbox servers, its Windows store version or EGS to account but I doubt their numbers are no different if not less then what Steam is reporting.
To remind people why free 2 play is risky venture is that you need money to run the serves, pay people to maintain it, other associates fees and of course make a profit. Unlike the old school subscription service of online only games, they get your money upfront before playing the game, guaranteeing they will have the rent money for next month (and the profits), can’t say same for F2P as name suggest is free to play. So, they have to add a monetization system in order to make up not having subscription service. Out 100% player base, about 25% on average that will pay some amount in the game give or take, out that percent only about ~2%-5% or less are regular paying customers that most F2P relies on keep them afloat. You get to a point that income is low as overall player active count is down, over time at this pace closing them will eventually outweigh the benefits of running them, as it become cost prohibited to do keep them open and becomes unprofitable.
Then there NGS spike that bound to happen with in next month or so parading any speaks in G-Man voice unforeseen consequences that might affect launch of it. This will no doubt raise player count for sure but real challenge is not total count… but continuous active player count is real challenge as it seems from Steam, other than some decent events that bring players back, game by itself can’t hold it players in meaningful way like its competitor FFXIV online which can average about ~20k day give or take.
With unified servers, both JP and Global will have to be maintain and at very least keep Global alive, granted it might be JP side covering the tab for some time before Global be able to pull its own weight in but at very least it will be better player experiences as there be more player active to work with then Global current state of affairs.