Also an option. We just have to keep in mind that we more or less already picked a side once this turn is over. This gives Smilnay a political advantage within the sector and in regards to whatever politics are played within the AdMech.
The most annoying case I could imagine would be the Ecclesiarchy siding with Milan, who would certainly accept the offer to deny Smilnay any political advantage over them.
This would give us the following "factions:"
Smilnay, Mist Shrikes and the Imperial Guard
And on the other hand...
Milan, the Ecclesiarchy (maybe) and the Navy (big "?" here since the Navy is currently in a power struggle)
Still, it wouldn't be a pretty picture politically.
As for hiding our Volkite tech, that would probably involve never producing or really using them. It's likely known that Severus has a Volkite sidearm. If we suddenly showed up with 5 more Volkite guns, then some heads will definitely turn. If said numbers increased
again then the AdMech could only conclude that we either found them on our planet or found an STC to build them.
Not sure how that would go. Even with Smilnay, whom we would be "allied" with. Space Marine Chapters are extremely indipendent and some tend to have their own technology seperate from the Mechanicus. But those are First Founding Chapters like the Blood Angels (Baal Pattern) or the Dark Angels. (As far as I know at least)
Right now I'm still tending towards giving the designs to Smilnay at some point (Could be 50 years. Could be 100). With what is written in the informational threadmark and what the QM wrote it appears to be a surefire way to get Terminatior Armor or other stuff. Depending on how this whole thing develops politically (the Ecclesiarchy) it might even become needed.
We'll see though.