@XComFan419: The stuff I learn by playing XCom..! Thanks for the info, it was super easy to find on wiki now!
@HelmetHair: Cool stuff!
One thing to state at the beginning: I don't like the idea introduced in the new XCom of chopping off limbs from people and turning them into cyborgs. That's not XCom to me, that's Robocop and borders into 40k dreadnoughts (except it's done on healthy soldiers instead of wounded/near death ones, so it's even worse).
XCom is not a distopia, it's a utopia of everybody working together to stop the aliens (until some cowards sign treaties, at least). It's not based on a setting where life is cheap, it's in the early 21st century where human and animal rights are pretty strong.
So I won't go about chopping dogs or giving them metal teeth. I think at the beginning of the game, they have a place as attack dogs, especially once up armoured with alien alloys. But once the mid-game aliens enter, you don't send the dog to take out a snakeman and especially not a chryssalid. There's no way even an alien alloy set of dog teeth should compare to the damage inflicted by a laser/plasma shot and that's the kind of damage needed to engage those. It's even worse against mutons and especially ethereals (who could just fly up). So the roles of dogs need to change to scout and logistics, hence the doggy senses and carrying capacity.
Now onto tanks: I like the idea you are suggesting with the tank and turret progression. It's sort of what I was trying to do with the alloy hull allowing progression of the tracked tanks so they do not become obsolete so fast but I agree it needs more tiers. 10 different hulls (5 tracked, 5 hover) and 15 turrets is A LOT though, even by restricting the compatibility, you have about.. 50 different tanks in your proposal. There's no way a player would come close to using all of them.
One thing is, if you have too many tiers, a player doesn't spend enough time in a given one to make use of it. It would be easy to skip tier 1-2 tanks and go straight for 3, then wait until 5 to renew the armoury. Much like some players skip lasers to go straight for plasma in the original.
I think I'll take 3 tracked tanks (basic, alloy hull, heavy alloy hull + elerium engine) and 2 hovertanks (one equivalent to the best tracked tank, one better but really expensive). That brings it down to 4 tiers and 5 chassis, with T3 tanks seeing the most use.
I prefer the final hovertank to be better armoured except for under armour (because it doesn't feel gravity, so armour weight doesn't matter, but the lower part is taken up by more vulnerable anti-gravity devices). Armour could progress simply by tiers. The tracked tank would have better accuracy (it is on the ground, so it is more stable). Our understanding of anti-gravity being recent, our hovertanks are a bit wobbly.
This way you have a trade off of having great firing lines by being high, or great accuracy by being on the ground, no tank is the perfect sniper. Flying makes you more visible, but with the T4 one you have better armour to compensate. And if you hug the ground with your T4 hovertank, well you're an expensive, slightly inaccurate but up-armoured tracked tank. Seems like there's no clear winner that way. The more I think about it, the more I want the hovertank (at least the T5 one, maybe all tanks with Elerium Engines) to blow up like cyberdiscs too.
Also, vanilla hovertank+25% armour is 130*1.25 = 162.5 armor, even heavy plasmas would have a hard time with it, especially if using TftD formulas. I don't think tanks need to go much beyond 130. That's not taking into account damage modifiers, at 50%, no plasma weapon could scratch a tank (heavy plasma is 115 damage, 230 max with EU damage formula, half for the modifier is back to 115, less than even vanilla hovertank armour, let alone boosted one). Aliens have to be able to kill tanks and I don't think tanks should rival sectopods in terms of armour.
Regarding turrets, stun and breacher weapons are great ideas, and you missed Gauss
Making a "limited but sufficient" selection of turrets and hulls is tricky. I wish there were a way to make it such that you can define a manufacturing project "Assemble tank" that takes 1 hull and up to 2 weapons and makes a tank, without having to define every possible combinations one by one, with associated assembly and dismantling. I would be easy enough to program (if only I knew C++...) and diminish the required modding work significantly.
