Alright, I currently have 4 CXP ranks up to max: Diplomacy, Development, Medical and Trade.
I've been running DOFF missions with my main character since day 1 of the Duty Officer system, and I'm about to hit rank 4 with 4 other skills. The new Jem'Hadar/Cardassian DOFF missions with much higher amounts of cxp have really sped things up.
So anyway, I'm hoping the system will be expanded to Rank 5 soon...
On a side note, Colonial and Recruitment are going MUCH slower than the rest of the commendation ranks, so that might need to be addressed soon too.