Yes, if all you want is just more points than the Xenos pack, you can buy just 5 Big Boss packs - you can buy all the cosmetic weapons/armor/utility items. But if you want to buy EVERYTHING in the store right now, you'll need a 6th pack that gives at least 10,000 points if I remember right. 5 of the BB packs can buy everything except the limited edition faction banners - which unless something has changed this morning they don't have pictures of yet.
That news to me. I don't see why Necrons should be an NPC faction. The only "mindless" units in their army are the basic Warriors/Flayed Ones. Everything above (Immortals, Deathmarks, Praetorians, Lychguards, Crypteks, Destroyers, Lords) have personality and individuality. And saying that these are elites and thus not suited to being played is ignoring the fact that the Space Marine faction is entirely made up of elites. In fact, I find IG to be the least likely faction to be ever implemented, since they are supposed to be a "fodder" faction. Not to mention the problem of them having to fight loyalist Space Marines.
I don't mean to sound like I am back pedalling, but I think you are right on about necrons being playable. Their more recent lore updates have made them a far more viable faction for this kind of game play (although I could imagine EC having to break alot of new ground to get customisability of individuals working, like different kinds of weapons and such) Maybe they would have a similar construct to eldar with the more classes, less flexibility for each class. I also agree that IG are the least workable, and in fact have argued that they shouldn't be brought in as a playable race at all. Not because I don't like them but because I would rather play a game with IG done well then IG shoe horned in just so everyone can feel like they are included. I want an IG FPS because I think that would match the feel of being a guardsman much more than it would in this setting. But these devs have done well at finding ways to make the asymmetrical balance for the 4 races work so far, maybe it could work for IG to. My main point is that there is sooooooooo much content that you can fill out with 4 factions and a 5th NPC that introducing the next race on the list so early would feel rushed. I wouldn't be said, I already have a 5th character slot ready to go, but doesn't feel logical to me.
If we're discounting DE as a 5th faction due to the presence of CWE, I'd favour Necrons over Tau anyday, and DE would be my first choice due to personal preferences...but moving on from that... Necrons have that wonderful egyptian terminator thing going for them, with enough model types to fill the class slots and then some While the Tau are melee weak (Kroot dont really count) and have a over-reliance on heavy armour suits/tanks to make it the powerful ranged army that it can be, IG are well...just humans, again they would need way too many armoured vehicles to hold their own fluff-wise on Arkhona,
You also seam to forget that the basic Tau gun (Pulse Rifle) is more powerful then any other factions basic weapon. While yes Tau are week in close combat they are better at range than other factions. This is a balancing factor. Like Orks are better in combat and worse at range. Yes Tau do like their battle suites (and really why shouldn't they), they are not fully dependent on them. Fire Warriors with Pulse Rifles, Pulse Carbines, EMP Grenades, and Drones. This will make up the bulk of their force. Will they have battle suites, Devilfish, Hammerheads, and Sky Rays? I hope so. The thought of Pathfinders with marker lights lasing a target and missiles from heavy armor in the back dropping in just makes me giddy.
if heavier armour types and more powerful weaponary comes with a higher RP to spawn cost ..which is pretty much what the Devs have said elsewhere...as well as vehicles themselves being expensive in RP to spawn, then a faction thats reliant on such equipment will come with a higher RP2Spawn rate, which may result over time in seeing a greater percentage of such a faction being fielded in "basic" low RP cost equipment as the player/faction starts to suffer under the weight of RP accumulation vs RP expenditure, conversely... if we decreased the RP cost of such equipment to a faction then not only would the other factions cry foul but the faction in question would at times be able to field superior numbers of units/vehicles requiring the other factions to "match the ante" resulting in their own personal/faction RP pools to be depleted at an increased rate
Again though this would be Lore in its own right and that would also attract players to the Tau side. Its like the Eldar having more classes and being more specialized, everyone (for the most part) saw this and said "Yeah that makes sense." Its Lore and it helps attract more Eldar players. And I guess this is the main problem that needs a solution. Space Marines in any format, (DOW, TT, video games) will be OP no matter what. There need to be outside of the box solutions to this. Giving Tau and asymmetrical but balanced boot of Vehicles in my opinion would be doable. It might attract the World of Tanks of fans and Anime fans to the franchise and I think those guys would fit in nicely with our fan group.