In patch 8.4, Panzer I Ausf. C and Panzer II Ausf. G are rumored to appear along with the classic Panzer I. It seems the new branch will look like this:
Tier 2 - Panzer I
Tier 3 - Panzer I Ausf. C
Tier 4 - Panzer II Ausf. G
Tier 4 - Panzer II "Luchs"
Tier 5 - Leopard
Tier 6 - VK2801
The history of Panzer I is well known and documented. Let's have a look at the remaining two vehicles:
Panzer I Ausf. C
Panzer I Ausf. C has practically nothing to do with the "basic" models - Panzer I Ausf. A and Panzer I Ausf. B (both the chassis and the turret were different). It was a specialist vehicle, developed for the paratrooper units in order to be transported in the Messerschmitt Me-321 planes, based on the army request for a light recoinnesance tank of the 8 ton category. The vehicle itself weighted around 8 tons indeed, had a 30mm frontal armor (both hull and turret) and was powered by a 150hp Maybach HL45P engine, allowing the vehicle to reach up to 80km/h. The armament consisted of an unusual combination: there was a MG-34 machinegun, but there was also a special 7,92mm anti-tank rifle designated EW141. Its caliber is only 7,92mm, but it's a high pressure weapon and thus its penetration will be sufficient (it fires the Panzerbüchse ammunition, which can penetrate around 25mm at 300m, which means it'll probably have around 40mm penetration in game).
It's a rather new project - several were built around 1943 (although Wiki states that the development started as soon as 1939 as a cooperation project between Krauss Maffei and Daimler Benz, with the first prototype built in 1941). Wiki states that 40 of these vehicles were produced and they served along with 6 prototypes (some sources claim only 4 prototypes) and most (38) served on the western front during Normandy landings.
Frontal - 30mm (mantlet thickness 30mm + 30mm frontal turret armor)
Side - 15-20mm
Rear - 10mm
Weapon: EW141 7,92mm autocannon/machine rifle
Engine: Maybach HL45P, 150hp
Maximum speed: 80km/h on the road, 35km/h offroad
Panzer II Ausf. G
Panzer II Ausf. G from 1941 (manufactured until February 1942), also referred to as a VK9.01 (9 ton, 1st project), or Pz.Kpfw. II neuer Art, was an attempt to re-work and improve the Panzer II series in order to prolong their lifespan. It uses a different type of suspension with 5 overlapping roadwheels (in German "Schachtelaufwerk") and eventually led (over the Ausf. J) to the development of the Leopard. Several prototypes were built and subsequently around 12 vehicles were completed. Some sources claim they never saw combat, while other sources (H. Doyle) claim at least one was transferred to the eastern front and apparently used (as it was covered by a camouflage):
Panzer II Ausf. G was uparmored when compared to its predecessors and its frontal armor was cca 30mm thick (15mm on the sides). However, when it comes to armament and engine, different sources say different things (even though the performance is roughly equal): it was propelled by a 150hp engine (Maybach HL 45, or Maybach HL66) and armed with a 7,92mm anti-tank rifle, described in the Panzer I Ausf. C part. One development version was also armed with a stabilized 20mm KwK 38 autocannon.
Wiki states that its turrets were later used for fortification.
Frontal - 30mm
Side - 15
Rear - 15mm
Weapon: 7,92mm AT rifle or 20mm autocannon
Engine: Maybach HL45P (HK66), 150hp
Maximum speed: 65km/h on the road, 50km/h offroad