I have been thinking about coming back for a while now.
Recently logged in to our guild CasualActive and I noticed the only one actually still playing is Cobalt and everyone else either quit or left to join other guilds. The quality of life updates helped out a lot, but it's still a cesspool of extremely limited units needing months to get them where you want them to be, unless you bring out a fat wallet.
Now I think I can say for most players that Collabs are still a huge pull to the game and make people get interested again.
Realistically though, I think it might not be possible. We have missed so many reruns and older collabs, that the possibility of a new one is questionable. Heck, I was very surprised we got the Seven Deadly Sins Collab, because the collab prior was AOT, a gap of almost 10 months or so. Considering this to be the case, who know at this point we might not even get collabs again.
The incentive for a collab is definitely interesting though, because it attracts not only new players, but also veterans and older players, who might be interested in coming back again and with the 7.0 update, stay. A lot of the older players were whales, so it could be a thing.
The question is whether Gumi is willing to invest though, and looking at their revenues they should make a decision rather fast. It's not stagnant anymore, BUT TAC is still doing ok , games with much bigger budgets like Heir of Light are doing way worse and they even have a collab with Tower of God at the moment.
One thing I will say is that WoTV definitely pulled a huge amount of the Tactical-JRPG lovers and probably a sizeable amount of TAC players that moved on, as WoTV will likely have a much bigger lifespan considering the IP.
I will stick around for the anniversary and see what their plans are, but it's not looking very promising, well this has been a thing since the introduction of limited units only on every release though...
JP may have the same problem, but at least they have collabs to keep the community alive and the game attractive enough for new players to join and vets to come back. Also japanese people spend a f-ton more money.