I have managed to get my local gaming club into a bit of Kill-Team which is great news for me as it's my favourite way to play 40K. Last week I ran a Tau infantry list (7 warriors, 4 Pathfinders - 1 ion rifle- and a specked up XV8) and won convincingly, this week I'm taking my battleship list and am hoping for similar success. However, I don't believe Tau are the way forward in Kill Team, that award goes to....Tempestus Scions! Here's why...
Hit on 3+, against most things you are wounding on 4/5+ but ALL of those wounds will go through because their Hot-shot lasguns are AP3. With a save of 4+ they have a good chance of surviving return fire too.
Scions also have access to the Taurox Prime which is a Gucci piece of kit. It's robust, dependable and can be tooled up with all manner of bits. I think the Autocannon is a good bet over the Hot Shot volley guns to give you some anti-armour and the Gatling cannon is hell-a-fun if you give the Prime the Split fire USR ("Yes, 1 shot each at those 10 guys." odds are you'll kill at least a few things per turn!)
This leaves you enough points to buy 8 Scions (9 if you leave the Battle cannon on the Prime) which is enough to put up a good fight. With regards to other upgrades, I think giving a power weapon to the Sergeant is a waste of points, especially in Kill Team where every point counts. One extra guy is more likely to make a kill than the power weapon is. Similarly there's no point giving him a bolt pistol the only one I would consider taking is a melta-gun over the Gatling cannon but I'll get a few games in before I make that call.
I think this is a viable list and with a space seat in the Taurox it's also a bit Kill-Team fluffy (Yo, grab that guy!), I'll let you know how it pans out.