The Skitarii codex is out now, and love it or leave it, I think this codex will make a big impact on the game itself. While in reality its a small codex, it has several strong units that will fit into just quite a few different armies as allies. What I don't see, although I think its quite possible to do, (despite internet first reactions) is the ability to field it as a stand alone army. This codex was obviously meant to be an allied force.
Skitarii as Allies
Really, what other minimum requirements would you want in an army. In the Skitarii codex you are only required to carry with you 2 troop units. This is simply amazing as it can really open up your list on what you want to field.
What's even better..... 5 man units as troops. Do you need to get Onagers? Two ground support units for your troops means a minimum investment to get these guys in there. After all, Onagers really can be a very strong unit choice.
Lets Talk about Onagers.
Onager Dunecrawlers may be one of my favorite unit options in the codex. They are simply amazing, not because they are armour 12 (which is too light I know for many people), but because they can overlap their shields. An armored force of armour 12 can be the bane of many armies on the tabletop when fielded in mass. Give them a 4+ invul save right off in round 1 and you have a force that needs to be hit by concentrated firepower to get rid of.
So you need some serious anti-armor in your force? 48" S10 AP1 blast Nuetron Lasers rock. Not to mention that they have concussive as well. A couple of these and armored forces sitting opposite you can be melted down rather quickly.
Need some AA, well the Icarus Array has that in spades as well, with the ability to take down a target with intercept, and then again during their shooting phase.
2 squads of 3 Onagers, while filling up the points of your list, are quite powerful.
Sicarian Infiltrators.
These guys are the harassment force in your list. Neurostratic Aura giving a -1 to BS and Leadership within 6" is a very cool ability. This should make your opponent really consider their deployment, and although more situational in my opinion, anything that makes your deploy differently is often a plus.
Troop Choices
Here you have Rangers and Vanguard. My first thoughts are sticking with Skitarii for their 30" range. Picking off special weapons and other targets of choice is indeed a good option.
I think if you are going for a large Skitarii force, Vanguard will work much better.
Conclusions,
There is a lot of cool rules with the Skitarii, and I have not dealt with them all, nor every unit. (ruststalkers and the walkers). I am still gathering my thoughts about this new codex, and how it will fit in with my other armies.
To field Skitarii as a primary force, there are some gaps that need to be looked at. Psychic powers in the force, T3 can make this force hard to field, and a little tricky. However, there are plenty of other armies to ally with.
I personally like the options a Skitarii force can bring to the table. I can see them as strong allied forces, small primary detachment forces, or just a means to get Onagers onto the field (which I really like)
There is another more detailed wright up on Codex: Skitarii, that if you want to see more rules and what else it has to offer. check out Peter's Review here
http://www.talkwargaming.com/2015/04/review-codex-skitarii.html