If that JH-XX by Shenyang is a true fighter-bomber instead of a pure 6th-gen fighter, I'm thinking of a max takeoff weight of ~60+ tons for the JH-XX. This is judging by how the large-size, heavy-weight 5th-gen fighters of today are already edging closer to 40 tons of max takeoff weight, hence I do believe that the max takeoff weight of 6th-gen fighters should be well into the 40-ton range, or even approaching/crossing the 50-ton mark.
if there was a fighter-bomber sized JH-XX it would need to be long enough to accommodate a ASM and long range LACMs.
taking a 3000 km class LACM as an example, the Kh-55 is 7.62 m long, 0.53 m OD. This is pretty typical; a Tomahawk is about the same size.
The PL-15 is 4 m long, 0.2 m OD, and the J-20 weapons bay can accommodate 4x of them. Let's say that the weapons bay is 1m across.
To accommodate Kh-55 class missiles, you'd need to stretch a J-20 class fighter's weapons bay by +3.6 m minimum. The stretching will require rebalancing of the plane. But to be really safe, and to accommodate a 2nd pilot in the seat as the weapons officer, you'd probably want to stretch the plane by +4 m.
To avoid having to widen the plane to carry more than 1x missile (which wouldn't be worth it), you'd need to make the bays deeper and have a rotary launcher. The rotary launcher is a proven solution.
1 way to accommodate a large enough rotary launcher is to delete the side bays and add a 4x rotary launcher of ~1.2 m OD, dropping 1 missile at a time in rapid succession. The J-20 fuselage is at least 2 m wide to accommodate 2x Al-31 sized engines, so this is feasible.
At empty weight of 17k kg and 20 m length, its about ~1000 kg per m. Stretching it by 4 m is +4000 kg roughly; even though it'll be an empty weapons bay, it'll still require some fuel, extra fuselage structural support and the rotary launcher itself at the minimum.
So we're looking at something like 24 m long, 22000 kg empty weight, carrying 4x 2200 kg payload for Kh-55 class missiles, minimum. That's about Mig-31 and F-111 size, which is realistic.
Range: This is where a fighter bomber gets tricky. Mig-31 has 0.8 M, high altitude combat radius of 1450 km while carrying 2000 kg of munitions (4x R-33) and 16000 kg of fuel.
F-111 has similar ferry range to the Mig-31, so it probably has a similar combat radius too.
That's too short for the Pacific.
So you'll need to stretch the plane even more to accommodate more fuel. I'm not an aerospace engineer, but I can see that at this point you're looking at major changes like increasing the length even more, increasing wing area, etc.
