I would like to suggest the Junkers Ju 88 P-3 which is probaply the most usefull of the P series (in game) coming with 2x 3,7 cm Bk 37 and a big amount of ammo, Armor and defences.
What it is:
The P series are modified Ju 88 A-4 (which is allready in game) to carry: P-1 a Pak 40/Bk 75, P-2 2x Bk 37 (mostly unchanged A-4, P-3 2x Bk 37 more armor and Jumo 211 P engines (starting power 1500 hp at 2700 rpm)
P-4 Ausf. A carring a hand loaded 5 cm Bk 5 with 42 rounds P-4 Ausf. B (only 1 build to show) a drum fed 5 cm Bk 5 with 36 rounds.
History: With the ever more threatening russian tank army moving against the german attacks the call for more CAS was needed. While beeing more cost effective and having more potential per flight than bombs, cannons on planes are not easy to implement (big ones) so strong carrier planes were equiped with cannons from 37mm to 88mm of the Types Ju 87, 88, Me 410, and Hs 129.
The Ju 88 P series was more or less effective, planned to fight tanks and Bombers, the results werent that good, because the guns with the HUGE baskets made them slow and a nice target for enemy fighters and ground units.
Never the less the P series was used as Ground striker with overall good effect.
The P-3 series was sent to one squadron of the Nachtschlachtgruppe 1, 2, 4, 8 and 9 for night attacks on the eastern front, northern Norway and Italy
Why i would like to see it (or them) in game:
Germany is famous for those planes and they are liked by many players (the planes in game allready) and overall there are multiple planes like these in the different trees such as US, RU, JP, IT and Germany.
There are allready 3 planes with Bk 37! Yes i know but the Bf 110 G-2 is at 3.7, has 66 rounds, 1 gun. The 2 G series Stukas are practically the same, but most importantly they are not such a big plane with a huge amount of armor and defecive armarment (4x 7,92 barrles with 1600 rpm each and over 20mm armor). The huge amount of ammo is also very important cince unlike the Bf 110 G-2 it doesnt have any other Offecive armarments.
This plane would make a lot of fun shooting at tanks or planes with a fire rate of 320 rpm (2x 160 rpm) and a huge ammo load, a weapon probaply able to turn the tides!
More about the P-3:
Additional armor over the A-4 also consits of frontal armor in the new enclosed nose of the plane.(probaply similar to that of the Bf 110 G-4) as well as armor on the bottom to protect from groundfire.
Crew: 3 (pilot, radio operator/rear gunner, navigator/ventral gunner)
Length: 14.4 m (47 ft 3 in)
Wingspan: 20 m (65 ft 7 in)
Height: 4.8 m (15 ft 9 in)
Wing area: 54.5 m2 (587 sq ft)
Empty weight: 9,860 kg (21,737 lb)
Gross weight: 12,105 kg (26,686 lb)
Max takeoff weight: 14,000 kg (30,865 lb)
Powerplant: 2x Jumo 211 P engines 1500 hp take off power
Propellers: 3-bladed VDM variable-pitch propeller
- Maximum speed: 470 km/h (290 mph, 250 kn) at 5,300 m (17,390 ft) and 12,500 kg (27,557 lb)
- Cruise speed: 370 km/h (230 mph, 200 kn) at 5,300 m (17,390 ft) economical cruising speed
- Range: 1,790 km (1,110 mi, 970 nmi) with 2,896 l (765 US gal; 637 imp gal)
- Ferry range: 2,730 km (1,700 mi, 1,470 nmi) with 4,028 l (1,064 US gal; 886 imp gal)
- Service ceiling: 8,200 m (26,900 ft)
- Time to altitude: 5,400 m (17,700 ft) in 23 minutes
- Wing loading: 220 kg/m2 (45 lb/sq ft)
- Power/mass: 0.100 hp/lb (0.164 kW/kg)
- 2 x 3,7 cm Bk 37 (90 rounds each or overall i am not shure, but 15 frames a 6 shots, cince 15 is a number you cant divide by 2 i guess its 180 rounds, 90 per gun?)
- 2 × 7.92 mm MG 81J machine guns on flexible mount in the rear of the cockpit canopy, firing aft with 1,000 rounds each. 
- 1 × 7.92 mm MG 81Z twin machine gun on flexible mount in the rear ventral Bola position, firing aft with 1,000 rounds.  
Ammo for the Bk 37 would be the Pzgr H (in game) Minengeschoss (In game) and the Pzgr 18 (found on the flaks in game allready)
Unlike visible on the drawing, the 2 Bk 37 are actually the only main guns of the P series which face forwards and not a bit down (this can be seen on the pictures of the planes).
Aircraft of the Luftwaffe 1935-1945, Jean-Denis G.G. Lepage
The Warplanes of the Third Reich, William Green (1972)
Junker Ju 88P, Rickard, J.