I want an RPG.
That takes place in the 40k universe.
Inspired (at least in part) by Bioware.
You start the game as an Inquisitor-in-training. There are no character classes for you. Instead, you assign points for skills and traits, and you gain more points as you level up. These determine your abilities in and out of combat, allowing you to build your inquisitor in any way you desire.
After a series of introductory missions which serve as a tutorial as well as kicking off the plot, you become a full Inquisitor and are allowed to pick from one of the three Ordos: Xenos, Malleus, and Hereticus. Each of these have unique bonuses and penalties, possibly special equipment as well - for example, joining the Ordo Malleus might gift you with a warded hammer that deals extra damage to daemons. After your initiation, the game world opens up and you can travel to various locations in order to resolve the main quest line, take side missions, etc.
In your travels you can make use of two primary types of NPCs: Contacts and Companions. Contacts are gained by interacting with people, gaining their service in a variety of ways from sidequests and payment to simply flashing your rosette. Contacts serve as your eyes and ears in places you cannot be and can provide valuable services, but (most) do not explicitly join your party. You also have some contacts after starting the main quest, dependent on which Ordo you joined and consisting of existing servants of the Inquisition.
Companions are your classic RPG party members. They travel alongside you and aid you, both in battle and out. At this point, I'm unsure as to whether they should be Bioware Companions (unique, having their own personalities and special quests and the like, cannot die outside of very specific circumstances, possibly romancable) or more like randomly-generated hirelings (which can die at any point, perhaps quite easily, but you can always get more). Both variations have their merits, and personally I'm sorta leaning towards the first option.
The morality system is absent from this game, because let's face it; you're an Inquisitor, and you may do whatever is justified. Instead, the game offers an alignment system. Depending on your actions, you may be viewed as a Puritan, a Radical, or anything in between. Puritans tend to favor the no-bullshit approach - you flash your rosette, you command with authority, you purge everything even slightly unclean. Radicals tend to favor subtler means of getting what they want, and depending on how far you are willing to go this may involve working with psykers, aliens, or worse.
Your reputation will oftentimes precede you, especially among fellow Inquisitors, and many will treat you differently depending on your abilities and where you fall on the scale. A Monodominant Puritan, for instance, might regard a psyker PC with barely-concealed scorn. On the flip-side, a Radical might hesitate to approach a strongly Puritan PC with information gained through "questionable means", for fear of denouncement. Companions are also impacted by your alignment, and doing something that they strongly oppose may result in them leaving or even turning on you. Perhaps some companions would only be willing to join you if you have certain reputations.
Combat should feature a fluid mix of both ranged and close combat, given how the setting is often portrayed. Since the PC has no defined class, they can become equally proficient in all things or choose to specialize. Companions, whether Bioware or hirelings, would be more rigidly defined but still with some wriggle room due to the skill and trait systems.
One thing I most certainly would want in this imaginary RPG is the presence of Untouchables. Either there needs to be an Untouchable companion, or the player needs the ability to make the PC into one at character creation, using traits. Being an Untouchable has a few huge benefits - no psychic attacks can hurt an Untouchable, and getting close to an enemy psyker shuts down their ability to draw upon the Warp - but also severe penalties in the form of massive (and permanent) debuffs to your charisma-based stats and abilities. You also would be unaffected by friendly psyker powers and could shut down your own psyker companions by getting too close.