The premium shop needs to be reworked completely and cloaks are just one of the things that need to be added - I'd add even stuff like the 2015 Christmas outfit or colored title if the price is high enough (the older the item, the higher the price) - I actually own both of these (got the colored title in 2015 event as well), and even though I'm a collector and I like the fact that I have something that's quite unique, I'd be okay with whole server having those if it meant getting rid of the paid dualbox. Because this is one of the main reasons the server is not growing, if you lock the dualbox behind paywall and force newbies to farm solo in completely empty low level zones, you don't have to be a rocket scientist to figure that server won't grow.
So: add cloaks, add more accessories, add some soft P2W stuff like +10% XP/SP runes, but make a second window free (PA required only for 2 or more windows... It could also give some basic XP/SP/Adena/Drop bonus as well, literally anything is better than forcing newbies to play solo without buffer)