I'd like some feedback on these Talents I mocked up for a player that desires to go for Two-Handed weapons, but feel that the support for it is underwhelming in comparison to Dual-Wielding.

I find myself agreeing with him, but at the same time at odds on how to make it happen. First because Two-Handed weapons tend to be a cut above other weapons, but also because there simply aren't that many options in the WH40kRP line for two-handed weapons.

This is what I came up with so far:

Aerocharge
Tier: 3
Alignment: Unaligned
Prerequisite: Operate (Personal) +10, Raptor, Fearless
Many that call themselves raptors, those warriors of the Ruinous Powers that utilizes a jump pack to rip and tear into their opponents, learn to master the art of the aerocharge. During an aerocharge, the character must perform an act of airborn flight with the help of a Jump Pack (or similar equipment), performing the end of a full Charge Action from at least 4 metres in the air.
Upon reaching the intended target of his Charge, he attacks all opponents adjacent to himself (including the intended target), resolving the Charge as normal against each of them. However, the character can only make a single attack against each, even if he has the Two-Weapon Wielding Talent, although if he does, he may choose which weapon applies to which opponent. The effects of this Talent cannot be combined with the Raptor Talent.

Reckless Thrashing
Tier: 2
Alignment: Khorne
Prerequisite: Strength 50, Agility 40, Frenzy
Many are the soldiers of the ruinous powers that eschew what many have called the finer points of combat, either because they trust in their natural ability so much that they think they cannot fail, or because they simply do not care about their own well-being.
At the beginning of an attack action, any Character with the Reckless Thrashing Talent wielding a two-handed weapon may declare that they will reduce their Weapon Skill and Agility for the remainder of the round, impacting both the upcoming attack as well as any reactions taken. When doing so, the Character receives +2 Damage for each 10 Characteristics he sacrifices, to a maximum of 50/10 (Taking a -50 penalty on all Weapon Skill and Agility Tests until his next round, but doing +10 Damage on his Attack(s).
This reckless thrashing can only be performed with the All-Out Attack, Standard Attack, Defensive Stance or Guarded Attack Combat Actions, but does apply to any Counterattack performed as part of a Parry.

Full Swing
Tier: 1
Alignment: Khorne
Prerequisite: Strength 40, Weapon Training (Primary), Ambidextrous
As a general rule, when any warrior fights with a two-handed weapon, the offhand primarily acts as a balance between the weight of the weapon and the movement of the main hand.
Through training in countless battles, the Character has reached a mastery of arms, rarely or never needing to use the extra hand for control, following every swing through with expert care. Whenever he wields a Melee weapon with two hands, he adds one-and-a-half of his Strength Bonus to the attack damage, rounding up, instead of just the Strength Bonus.
Thus a Character with this Talent that has a Strength Bonus of 5 (50 Strength) adds 8 Damage to his Melee Attacks instead of 5.

I would make Full swing a flat Unnatural Strength bonus as BC went out of its way to eliminate the multipliers from the system.

The two Two-Handed talents sound very much like DnD, so this is somewhat about character continuation with that player?^^

I also do agree to make Full Swing a flat bonus that scales and not multiplies. Also I'd make it a T3 Talent for it works very much like crushing blow and honestly roughly does the same.

Also I'd make being frenzied a requirement for Reckless Thrashing though it is flat increased damage then (again) for you sacrifice your +10 from frenzy for a simple increase.

To compare it with dual-wielding is kinda hard imho. As a dual wielding you mostly spend xp to shrug of all those negative modifiers with a pretty linear T1/T2/T3 combination. In the end you are a pretty competent fighter but you had to heavily invest into it. Two-Handed weapons in my opinion were mostly good starter weapons but got decent later on - and intended to do so. But yea, nothing speaks against some buffs if that really is what you wish and your group can handle such custom rules (Which is the biggest problems, at last in the groups where I was player). Also the lack of dedicated two-handed weapons is not that severe for many one-handed weapons have additional rules for being wielded two-handed. And in that regard a shocking and concussive Power-Maul that gets swung around with your even more increased damage on a lightning attack is rather intimidating.