I was encouraged when the Cult Mechanicus models were released. With the exception of the Electro-priests, Cult models are reasonably durable and worth quite a few points. Since Skitarii and Cult Mechanicus are obviously designed to complement each other, I ditched the idea of a pure Skitarii army in favor of a mixed Mechanicus army. With the release of the Adeptus Mechanicus War Convocation Formation in the recent White Dwarf, I began to develop a Mechanicus list around the new Formation.
The War Convocation is composed of a Cult Mechanicus Battle Congregation (1 HQ and 2 Troops minimum with the option for 6 more Troops, 0-4 Elites, 0-2 Heavy Support, and 0-1 Fortifications), a Skitarii Battle Maniple, and an Imperial Knight Oathsworn Detachment (1-3 Imperial Knights). Where the Formation goes entirely insane is in the Might of the Adeptus Mechanicus rule:
All weapon and wargear options taken by units in this Formation, including any Relics of Mars or Arcana Mechanicum, are free. Furthermore, all weapons with the Gets Hot special rule carried by a model in this Formation no longer has the Gets Hot special rule.
For 1985 points (I was unable to get up to a full 2000 points), I built a list that included a Tech-priest Dominus, one Kataphron Destroyer Squad (3 servitors), one Kataphron Breacher Squad (4 servitors), one Kastelan Robot Maniple (1 datasmith, 2 Robots), one Vanguard Squad (10 men), one Ranger Squad (10 men), one Ruststalker Squad (5 men), one Infiltrator Squad (5 men), one Ironstrider Squadron (1 Ballistarii), one Onager Squadron (2 Dunecrawlers), and a Knight Crusader. Alternatively, I could swap out the Knight Crusader for a Knight Errant and take an additional Kataphron Destroyer servitor. Of course I took advantage of the free upgrades, loading the squads up with quite a few options. I would have added more upgrades, but I'll be integrating models into my existing army as I finish them. It could be a very long time before I can play a full War Convocation and I won't be able to take advantage of the free options until then.
Out of curiosity, I calculated how much free stuff using the War Convocation Formation would give me. The cost difference turned out to be a full 395 points, which is more than the cost of most Imperial Knight patterns. [Correction 5/31/15: It's actually 430 points; I forgot to add in the Knight's upgrades. That puts the value of the Formation at that of a Knight Crusader with a battle cannon.] In other words, the Formation is fantastically broken and will almost certainly be one of the most common ways that Adeptus Mechanicus are fielded.