@zombiegenesis Consider the issue with dinosaurs, for example. You run your game for 6 months when I come in; at that point everyone is 6 months ahead of me in terms of power - and there are no diminishing returns in nWoD 2.0 either; the fifth dot costs as much as the third dot does. In six months they will still be six months ahead of me, and I can never catch up. Are there catchup mechanisms? Is this situation acceptable? It might well be, but you need to plan in advance for it.
Or alternatively think of the power curve. We both start playing the game, but I just happen to have way more time than you, or have more OOC friends allowing me to participate in more PrPs or any combination of such factors, so I accumulate XPs a lot faster. How much more powerful ought my PC be than yours? That's a question you need to have an answer for.
The third scenario (which was popular on TR) - people created XP containers. They'd make say, a Mage they didn't plan to play at the time and keep them there for a rainy day, since they'd gather XP just by existing. Is that okay? Isn't it? Same question. 
Just some food for thought.