@Enjou can you please divine the fortress of the Soulless?
My reasons
1 tech trade with the assassins guild would benefit both of us. Or even just give them a copy of the tech we have to keep for when the Emperor comes back.
2 the Silent sisterhood also has tech we could use such as "null iron". Again trade between both of us would help each other.
3 they have to have someway of traveling around the galaxy in order to try to bring order to the galaxy.
4 they are trying to bring order to the galaxy and coordination would help everyone.
The following reason are based on my theory the Custodies are there.
5. the Custodies are there... maybe. Which would mean that we could ask them for help with Saint Lin. They spent 15,000 years apparently being a order that guarded the golden throne and being scholars. If any human faction will know how to help it will be them.
6 the Custodies literally have the most advance tech the Emperor could find and design. Imagine upgrades everything the Soace Mariens has and than some.