I like it! Although, just to clarify (because we've discussed all this as well) - the idea is that this is not 'another' department: because we can hardly manage to keep 2 out of 3 active at the moment, so adding a 4th is madness, because 3 is a wonderful number, because 3 is the 'tradition', and because the Deathstalkers/Apothecaries/Deathguard are the 3 'standard' branches of the Forsaken war machine represented in Lore. HOWEVER. What it definitely is, is a sort of 'group' which, as Elli suggested, will operate as part of the Guild and include members from all of the 3 branches (most commonly the Apothecaries, I would presume) and those who aren't in any of the 3 branches.
The very best analogy is what Geri aimed to do with the Cult of the Forgotten Shadow. He led occasional sermons, and he had a handful of clerics or devotees to the faith under him - but they were often also part of one of the 3 departments. Hope that's clear.
And, with that explained, I thoroughly approve this idea! Viatrix herself will most probably be able to contribute and I hope to see some concrete events soon (because planning is dull, and doing is fun)!