Hello. Not sure if anyone is going to read this to be honest given the state of things currently. However, I think there are a few things that need to be addressed (which should be simple enough to do as they already existed):
First, the change on JP regarding Rainbow Keys from recommended chests needs to be added to global/NA. Otherwise we lack the ability to obtain them AND some of the unique rewards within.
Second, the limited AC Swap reward shop in global should be cycled in and out still. It has unique options that are otherwise removed entirely.
Third, some affixes such as Reaper: Weak to Fire and Reaper: Weak to Lightning were apparently never added to NA. This seems odd and wouldn't be all that complicated. For that matter, there is a fair amount of content still on the JP base version that could be ported over to NA. While translations might be a little work (cannot say there myself) it would be minimal work for quite the fair bit of appreciation. For example, the instruments for private quarters like the baby grand piano, drum set, and so on. Or the rest of the weapon camos.
Four, still cycle in the improved boost weeks to base. This wouldn't take anything at all and would be good for engagement.
There is a LOT of content in base. But its these small things listed above that would help to keep things lively while requiring minimal effort on the side of corporate. The unique situation where you have both games connected and running offers a great opportunity for you. You seem to be doing bursts of content in NGS with 6 month periods. And the base lobbies are still quite populated given the lack of things to do in NGS. I guess what Im trying to say is that there are ways to minimize resource drain while encouraging your consumer engagement.
Finally, as a personal note, I think adding private quarters to NGS would have great results. That or find ways to engage alliances more. You seem to have taken an open world approach without considering the player base interactions. Essentially, what Blizzard did to crash their player base. And, quite frankly, you don't have the same starting size of player base to risk losing.