We aren't getting to anywhere actually, we started discussing old things while we should be discussing the current problem. And as a main question you have will "Epilogue be of any use to population growing or will it be another addon of Lineage 2".
I'll have to answer yes, It will be nothing special a rise in popularity will not occur until something in the game really changes . Will L3 Save it then? Can't tell we don't even know how it will look like so we cannot really tell. But you see there's still hope i'll allow myself to quote a Bulgarian philosopher "For something new to be born something old should die." You could translate it as you'd like. It's a 50/50 option for Lineage. Either it grows after Lineage 3 either it dies.