Grindea as MMO could do with it's content (at least when finished), but with some tricks. Drop rates could be
drastically decreased and new items added for enemies. Also some items could have special conditions to be dropped, like killing enemies in order. Then, difficulty steps for areas should be increased, so you have to level hard to progress. And level cap could be way higher (if not unlimited). Players could level for some PVP swag if no content is left. And some simple enchanting system, everyone wants their weapon upgraded to +15. Additionally, some daily quest with special rewards after completing it 100 times.
Such changes can artificially increase length of the game, leaving players with hundreds of hours of pointless grinding. Well, it's not an idea for enjoyable game, but good used, may generate much profit. Of course with online shop with potions that double experience gain or drop rates or some unique outfits for your char. But that isn't going to happen, since SoG is made to be enjoyed, not to generate cash