Additionally the promotion of 10 Commanders to serve on one ship feels too outlandish! You as the Captain of your own ship start as an Ensign. You gain your first BO during the tutorial with others soon to follow. BO start at the rank of Ensign but cannot be promoted until you the Captain reach LTCmdr.
How the promotion process should work:
(Captain Rank) Ensign=(BO Max rank) Ensign(Tutorial promotion of Officer from Crewman to Ensign)
Lieutenant=Ensign (0 promotions available)
LT Commander=Lt (4 promotions + reduction available)
Commander=LTCmdr (7 promotions)
Captain=Cmdr (10 promotions)
RALH/BG=Cmdr (12 promotions)
RAUH/MG=Cmdr (13 promotions)
VA/LTG=Cmdr (15 promotions)
In order for a BO to merit promotion they must improve their performance. Using the current skill point requirement for a promotion. BO skills are not rank specific however and you can apply skill points to any Skill the BO possesses.
Reducing a BO grants you back the promotion so you could grant it to someone else. Discharging, Trading or promoting to Captain grants you back your slots. You cannot demote a BO until you gain LTCmdr.
BOff skills should be more conducive to the Captain Skills but still split between space and ground. However, they should be to improve powers like the captain not give them. Space powers would be generated by the ship and the BOff you assign to the positions on your ship.
You would be striving to find the BO that is best suited for what you need them to do. Planning the skills that you want your ship to have you would be looking for a BO to assist you in maximizing the effects of those powers.
Ground powers come from the same place as your captain, Kits! Even though you are using a Ensign on your Away Team doesn't mean you should suffer the loss of those powers. This would be allowed through the use of kits. Kits, like shields, weapons and armor are based off the level of the PC (Player Captain) not the character wearing the gear.
I think of BOff skills in this manner as what they specialized in at the academy or what they are best suited in. Like in JJ's 2009 Movie when Sulu said he is specialized in "Hand to Hand Combat" because he is a good fencer! I picture a Science officer choosing Medical over Chemistry, Astrometrics over Photonic Theory.
BOffs should all have 1 space trait and 3 ground traits. Traits are what truly make a BOff common or very rare. This should not change. Common=2 basic traits, Uncommon=1 basic trait, Rare=1 Superior trait, Very rare=2 Superior traits.
Skill points are used to improve the effectiveness of powers for the BO. BO skills are not rank driven though and points can be placed into any skill at any time to improve it. For this reason it is conceivable that you would still be able to max out all your BOffs skills even if the BO is still an Esn.
How the ship function:
10 assignments on the ship for your BOffs to fill. Filling those functions opens up the space powers based on the BO to fill them. The level of power would still be based on the BO filling the position. A Cmdr gets 4 powers while a Esn gets one. Esn and LT have access to level 1 powers while LTCmdr and Cmdr have access to level 2 powers. A Captain can train a Cmdr BO in Level 3 skills. (current system) By applying 9 skill points to certain skills the captain gains access to level 3 powers.
Color denotes power selection not the type of officer to fill the position. All position are "Universal" however the BO skills affect only the powers he is assigned to use. Thus assigning a TAC BO with Projectiles and Torpedoes skills to be your TacOps he would improve powers like Torpedo High Yield or Torpedo Spread.
Where BOffs are accepted as crewmen and need to be promoted to Ensign this will limit the number of "powers" a ship has.
I think this would ultimately assist in placement of proper personnel into key assigned positions where they are supposed to be positioned on the ship. So as you go through your ship you will be able to address them accordingly.