Yes you've played for two months and gotten all this sweet gear. It's the top of the line.
And now you have one gem, but wait! You still have 9 slots left! Now you will spend another 2 months collecting enough gems to fill another slot! And another! And another!
Now they are all finally socketed but you do have 10 gems that can be removed.
But what if those gems are also used in crafting recipes? What then?!
The problem with wanting it to take two months to get to the top rank of gem, is that it is unrealistic unless the gems served only one purpose. Which is unlikely to be the case from what I read.
Not that the crafting idea will not be unrewarding or anything about the idea will be unrewarding. The likelihood of it being rewarding enough to justify two months for a singe end game gem, and don't fool yourself into thinking it's purely on the side, once you're up there, and you have practically the best gear there is you'll want the best gems there are, and if it took less time to get the best gear, then it took for the gem upgrade, the upgrade must be worth it.
I'm not saying the gems won't be worth an insane amount of effort, try and remember that. I'm saying they must be. Gem collecting eventually won't be something you simply do on the side of everything else. And when you get to that point the amount of time it takes needs to be worth the reward.
The likelihood of anyone wanting to spend two months gathering materials for a single crafting recipe is unlikely unless it's worth it. It must be worth it or it simply becomes a broken system.
Of course I am potentially talking to people who would be totally willing to go find a legitimate Sealed J Sword in PSO, and spend over two thousand hours doing it, and calling it worth it when all you could do is grind that same level over and over again to even have a shot.
And really if you're someone like that, just tell me now. I don't have the energy to talk with someone quite that much of a fanatic.