There's a bunch of species classified as "Constrictor" snakes, and you suggest the path based on crushing be named "elite"...

I don't take LW2 as gospel, but "Sidewinder" is a term derived from the way desert snakes move to achieve their amazing speed in an environment where there is no irregular terrain to provide traction. Why would a path named like this be focused on biological weapons, when the natural connection that springs to mind is mobility?

The above is doubly questionable when you realize that the Cobra/Naja is the snake family famous for it's particularly potent venoms, and some members of the species ability to spit it's venom at range with great accuracy.

What you request isn't QoL(Vipers no longer breaking the game when you make them hack something is), it's a request to recreate the mod to your specific vision(one with which I immediately disagree simply because it is different from mine).

Just about the only new ability that'd be a true QoL would be some sort of manual release for the Bind skill, since there is no such feature in vanilla as far as I can tell, and it is something everyone would agree to be usefull. Anything beyond that should be content of another mod to be made by another person.

The author of this mod has yet to share or request any ideas as to how to improve the gameplay, and you can already edit the .ini file to alter the Viper's skillset, so this is a bit of a pointless coversation.
However, as far as "my vision" goes:
To take advantage of the new Training Center feature of WOTC, the Playable aliens should indeed have 3 distinct trees each, in a fashion similar to a faction hero unit.
Those trees should have a degree of synergy, and support a small ammount of semi-random XCOM abilities(right now, Vipers can get useless perks from the Training Center).

For a Viper, my "focus trees" suggestion would be:
Cobra: Abilities that focus on delivering poison: Venom Spit attack is moved here and no longer part of the default kit, spit upgrade to acid, poison on basic shots and squadsight perks are available here.
Rattlesnake: Abilities that allow the Viper to cause Panic, with upgrades that allow it to do it in response to being shot at, and/or without breaking Concelement.
Anaconda: Abilities that allow the Viper to take to the frontline and use Bind aggressively, such as gaining a shield when using it, and the ability to maintain it under fire.
XCOM randoms, 4 out of the following: Shadowstrike, Phantom, Conceal, Resilience, Run and Gun, Shadowstep, Low Profile.

I Just want a chosen on my team...even if its nerfed to hell to be balanced.

I really need ANDROMEDON :) want to spit some acid on 'em

@Dawn: unfortunately for you, the Andro isn't likely to show up, simply on the account of the poor bastards are stuck in environment suits, which would likely have kill-switches if they tried to go rogue. The Viper, Sectoid and Muton actually make a bit of sense, given all three are (a) mass produced, (b) are capable of thinking for themselves (especially the Viper, which likely is still capable of everything the Thin Man was), and (c) all have a lot more human DNA in them, meaning it's entirely possible the Commander's values might've passed into them (which is how i see Betos and her kind going rogue and immediately going anti-Elder).

I would suggest a transforming faceless, a powerful ambusher, able to take the shape of an advent soldier or a civilian when out of sight and take it's faceless form when they get close or on command. to justify it in the lore they have a gelatinous body makein it hard to place a kill switch in it like the Andro and is inntelligent enough to be an infiltrator, so it its not that big of a jump to be smart enough to rebel, they are clearly not an attack dog like the berserker or the chryssalid

@Arkangel

that is a shame :(

Sectopods. They may be walking tanks that turn the tide of a mission by themselves (aka OP), but damn do I miss them from the Playable Aliens mod.

@Arkangel
The kill-switch of the Andromedon could have been damaged in battle, like it happened to the chip of some Skirmishers. Or it could be eroded, because the psionic network has some stability-problems with the sudden disconnection of the commander. That would also explain why those aliens only recently start to act up.
The problem would be the rescue of the Andromedon, as it can't be the same way we get the Sectoid, Viper and Muton. Being locked in a cell or transport-vehicle won't stop an Andromedon as he could simply walk through them.
Perhaps a rescue-mission like you sometimes get for the resistance? With an Andromedon (or any other massive alien) being cornered somewhere and keeping the attackers at bay, but running low on ammunition, giving you a timelimit to reach them. Once you get to them, reinforcements start to come in. A bit like with the lost, only with proper ADVENT-Forces.
I mostly wrote that much text because I also would love to have an Andromedon (or Berserker) on my team.

Is it possible to have a mod where the aliens can join as effectively the rookie class (except with alien power perks) and then grow into the other classes? Like, a Viper ranger, a viper sharpshooter, Viper Psionic, (etc)? Based on what I see above, its probably not quite what you've got in mind, but I may as well put it out there anyways.
Also, I'm fairly certain this mod doesn't directly allow one to do full on armor customization/tweaks, nor really match the technological upgrades of the human soldier's gear upgrades in aesthetics; but it would be cool if it did... It would add a touch of realism and flair to have that though. I don't think aliens that desert their overloads are going to be able to keep their origional gear in working order too long.
That said, I imagine that only the class branching idea is likely to be easy enough to achieve if (as I noticed someone mention on the main page of this mod) you've only got a coder to work with rather than a modler.

Will there be a chance for us to be able to have a gatekeeper in our roster? I really like that unit.

How about adding the archon as recruitable units, make a new "Sectoid Ruler" (for Alien hunter DLC), and then (for alien hunter) have a mission on cornering(alien ruler can't escape) each alien ruler for each respective recruitable alien which will give one of your units a skill based off that ruler(except ruler reaction ofc) or some other improvement.

Muton Berserker, a tough melee combatan thats also risky to use since enemies could enrage him and set him loose on your own squad.

Mrvecz the Muton Berserker is a wild card. I think it attacks the nearset person while enraged. That being said I'd probably send her further away from my squad at the risk of her being overwhemled and killed. That 's usually how I killed Berserkers. Keep my squad together, move the blue step by blue step, activate a pod, Berserker takes a few steps to squad, move soldier if possible, then target practice. I like the idea of a Berserker ally, but she needs some good perks to ensure she won't die so easily. Also the Berserker should not appear inside Skyranger at all.

@Luna: stuff like that is going to take time, and the work of modelers, animators, and so on. not saying it isn't possible, but it'll take a dedicated team to do it. but we'll see where it goes over time.