The Dark Engine and the "Angelic" intelligences that guarded it have long stymied me, as they're a vital element of the setting but difficult to model well in GURPS. I've finally managed to work out all the various elements: How they interact with the Dark Engine, how they can keep up with Sci-Fi Knights in Power Armor despite paying gobs of points for their shells, and so on.
I really struggled with that last element. I envision the robots uploading themselves in shells like they do in Transhuman Space, except these are angelic, mythic shells made of awesome. However, Possession and Puppet rules require you pay for your "most expensive body." The shell I finally settled on as a "standard" combat shell cost at least 1000 points, 250 more than a Knight, and less effective. However, if I discarded this rule and allowed you to simply purchase superior bodies as puppets (15 points for that 1000 point body), following the logic that the body is really no different from power armor, I worried they would be "too powerful." Eventually, though, this worry turned out to be of no concern. A 750 point Angel with a 1000 point shell is about on par with a 750 point Knight with Power Armor and an Assault Cannon (a little weaker actually, and I'm ok with that).
However, this left the question of the Angel's "base" shell. If you can purchase a super shell for a mere 15 points, why bother to pay for any ST of your own? I eventually decided that in the Dark Engine, you have to use your "native" stats, and that your "base" shell (the standard looking robot) also uses these base stats. Interestingly, this discussion lead to an interesting idea:
The Angels draw their inspiration from Wraith and, indeed, most of the "Angels" are really uploaded human intelligences ("Ancestral Emulations"). While pondering the fact that you had these static stats that you lost when you changed shells, I suddenly wondered if humanity might be able to "exceed the limitations of their shells." All robots in a Seraphim Shell have exactly 18 ST, but what if some humans known for their strength got a little more out of their machine, and pushed it to 20 ST? I thought this provided an interesting mechanic allowing players to define their character a little more, and express their innate humanity in a way that the robots lacked. It also made humans "special," in a way that set them apart from their colder, mechanical robot kin. Finally, it tied into this notion that robots tend to see humanity as "special," almost worshiping their creators.
With that out of the way, I'm buckling back down on the core game concepts (the Knights and their kin) and working towards making this playable, as some local players have expressed interest in playing. However, I've finished Dawn of War II: Chaos Rising, so I have no idea how long I'll remain interested in this little project ^_^;;