How to become an Incubus

To build on your conspiracy idea, maybe try this? An Archon comes up with a plan to get his "own" Shrine, and raises a number of Half-born (suitably "modified" by the Haemonculi, of course...), with the purpose of having them join the Shrine themselves, all the while staying loyal to the Kabal. Eventually, as they progress up the ranks, one will become the Hierarch, and thus the Shrine as a whole will be 'loyal' to the Kabal.

Sadly, this plan backfired when the leader of the infiltrators decided he'd much rather be an Archon, and thus allowed his second-in-command (a better warrior than him, who was satisfied staying as an Incubi) to defeat the Hierarch in a duel. In the subsequent ceremony to deliver the good news to the Archon that his plan had finally succeeded, the leader stepped forward, and beheaded the Archon with his klaive. As this took place in the Shrine, and was a one-on-one fight, the winner took the organisation of the loser (usually the Shrine, but hey, are you going to argue with the guy with a Hierarch and dozens upon dozens of highly-dangerous Incubi behind him? If he says the Kabal is his, the Kabal is his), and renamed it as the Kabal of the Crimson Tear. As was planned, the hierarch stays loyal to the Kabal, as long as they don't get too demanding as to what's expected of the Incubi.