To engage with the OP topic though:
I don't think PSO2 really needs any incentives to actually play it though, because it is a game in its own right and it will be fun to play even with NGS out. Previous games don't just suddenly lose all their value due to a sequel coming out.
However, SEGA should really "unlock" PSO2 so to speak when NGS comes out. By this, I mean that all content should be playable and everything be farmable realistically without having to worry about time slots (Urgents) or heavy player numbers (how do you get 12 players for raid bosses when everyone is on NGS?). Having 4P content is fine, but even now 12P content is difficult to fill up.
There's also things like Grand Capsules, Mark Capsules, Mission Badge related stuff, Titles/Achievements, etc that should all be readily accessible to get once NGS come out -- lord knows I'm not getting the rematch Yamato titles any time soon since you... can't do them at all unless it's on the schedule lol, but something should be done about that.
Uncapping timegated stuff will also go a long way, or making their limits higher. Augment Passes, Mission Badges (although this is going), things like Crystals and Grania should all be uncapped on NGS release so it's just a grind, not a timegated grind, and you can just simply work on making perfect gear or niche gear or whatever you're interested in in your own time.
As it stands now though, PSO2 Global feels somewhat gimped and impossible to do things on, and NGS being in 2 months really knocks the motivation down, because what if all this timegated stuff ends up staying on NGS release? It will just feel really bad trying to play PSO2 to do whatever you like when nobody is playing it and you're still just sitting around waiting for daily/weekly resets or urgents.