I agree with most of what you said in there. I wouldn't dismiss the impact of adding even 200 km to combat radius. That extra difference could open up quite a few missions as well as doubling the loiter time over other missions.
I think you can probably get that with support for 3 large external fuel tanks, a little more bulked airframe and engines with better fuel burn. That along with more avionics upgrade might be enough for a new subclass.
I have a hard time seeing something like even a fighter bomber version j20 having space to carry a lot of fuel and payload internally. Just hard to achieve stealth in my opinion for a fighter bomber. Ucav would do better.
I agree that an additional 200km to its combat radius is not insignificant, but I think it all depends on how much aerospace resources and how much time it ends up costing.
In terms of combat aircraft (fighters, strike fighters, bombers), I am of the belief that any new clean sheet types or new subvariants of existing types for PLA service, that start development in the 2020s, should ideally have VLO.
In this case, a strike/longer range J-16 variant would be in the "new subvariant" category and would like take 2+ years to develop, test fly, and verify all of its parameters and characteristics. Such an aircraft could enter production in 2024-2025 and could probably enter full rate production equivalent pretty quickly.
But I personally can't see all of that being worth the finite aerospace industry resources at our present span of time in the early 2020s -- by that, I mean the full combination of engineering time, computing time, flight test needs, and the elapsed years and money spent -- for 200km of additional combat radius.
I do strongly agree that enhanced aerial strike capabilities at longer distances would be useful, but I think any such solution being developed in the early 2020s should be more survivable in the long term.
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Off topic, but for the record, I also believe that a hypothetical strike J-20 variant would be undesirable -- I agree that the fuel and payload it could carry would be... unimpressive and probably not worth the money and aerospace resources and time.
IMO, any new major regional bomber should ideally fulfill a few physical parameters/criteria:
- VLO
- ~2000km combat radius
- sizeable weapons bay for large volume payloads including relatively sizeable cruise missiles (ability to carry two YJ-12 missiles in volume equivalent) or a decent quantity of direct attack PGMs.
- small internal weapons bay for A2A weapons (say, two small weapons bays, carrying one PL-15 sized missile each)
- supersonic capable (supersonic dash capable for part of the mission, but not required to have supercruise)
Needless to say, such an aircraft would be excellent, but be quite expensive.
If they cannot achieve those criteria with a clean sheet design (and a strike J-20 variant most certainly be unable to either), I think it would make more sense simply to pursue longer ranged standoff weapons, VLO strike UCAVs, and H-20 for longer ranged targets, and to use standard J-20s and J-35/XYs carrying internal JSM and SDB equivalent weapons, for closer targets within 800km of the Chinese coast.
All backed up by J-16s, H-6K/J/Ns, that will enjoy new generation munitions, and the entire fleet being supported by aerial refuelling operating in the more secure "rear".