Any guess when they will retire the J-11?
I've heard rumors that J-11BG is not a comprehensive upgrade but just an antenna upgrade (Not even a full radar upgrade), which means it still uses the old backend paired with a new antenna like the APG-63(V)2 and possibly a software update to allow it to probably carry the PL-15 (?, as no evidence of it has emerged). Engines are upgraded but I doubt it's on purpose as it is more likely that the original AL-31F were worn out and were just replaced by WS-10As to simplify logistics neither was the avionic suite overhauled.
It's difficult to claim it's Su-35S level when Su-35S has a much newer avionics suite, much better engines, TVC for supersonic trim and it's PESA radar is extremely powerful due to raw average output power and probably a more modern backend.
Any guess when they will retire the J-11?
IMO, it would simply be easier to replace all of the J-11s, there are only 400 of them built and probably ~300 or so left in service, with J-20's production rate it is possible to replace most of the J-11 fleet with J-20As (or hand-me-down J-20s from units upgrading to J-20As) by the end of this 5YP. PLAAF is seemingly going to be accepting many manned aircraft in the coming years which makes sense for them to retire their older fleet (Newer aircraft would probably be given to training units and aviation colleges) unless they want to significantly upsize their combat fleet. Though I'm not sure how upsizing makes more sense considering the trend these days with drones taking the lower end tasks and possibly even taking up higher end air combat with UADFs.China has over 200 J-11B it can slowly convert to J-11BG. Giving them access to PL-15/16 and PL-17 even if via CEC dependent on other platforms is still a huge boost to combat capability for PLAAF. That's picking up an additional 200 units with 4.5 gen BVR capability with a relatively simple and inexpensive midlife upgrade. The J-11B was previously limited to PL-12 range with easily detected RF emission from its pulse doppler, making it only as good as a 3rd gen in most situations against any 4.5 or 5th gens. Now it can hold its own.
In a world where most second tier airforces barely have a handful of serviceable 4.5 gens that represent the absolute top tier of their fighter force, China is in the process of upgrading ~200 to closely match that performance level (actually exceed if it gets PL-16 and PL-17).
iirc there are still active J-11A unitsJ-11s are being retired and might be completely retired by now? Some J-11A units have reached retirement airframe life for the ones that were assembled in the 1990s and had more use put through.

IMO, it would simply be easier to replace all of the J-11s, there are only 400 of them built and probably ~300 or so left in service, with J-20's production rate it is possible to replace most of the J-11 fleet with J-20As (or hand-me-down J-20s from units upgrading to J-20As) by the end of this 5YP. PLAAF is seemingly going to be accepting many manned aircraft in the coming years which makes sense for them to retire their older fleet (Newer aircraft would probably be given to training units and aviation colleges) unless they want to significantly upsize their combat fleet. Though I'm not sure how upsizing makes more sense considering the trend these days with drones taking the lower end tasks and possibly even taking up higher end air combat with UADFs.
J-11BG conversions also haven't been very frequent AFAIK as very little were ever spotted in the last few years and most of the spotted ones were apparently the last two batches of J-11Bs that were factory built to the BG standard.
What else do you do with 200+ J-11Bs with between 10-20 years of airframe life left? CEC them with the rest of the PLAAF so it's performing BVR at least to J-10B/C and original J-16 block level.
They can also operate as trucks for glide bombs. In such a role, they would need only minimal upgrades.
There's no guarantee that J-11BG is capable of even carrying the PL-15 much less the PL-17. Upgrading old J-11Bs to be able to fully network with the rest of the fleet is going to take some major changes considering the original avionics were never designed with it in mind.I don't see why PLAAF should simply retire all J-11 series when the J-11B has so much useful life in the airframes and 5th gen PLAAF fighters cannot carry the PL-17 internally. If you network your J-11BG appropriately, you instantly get 200+ additional PL-17 shooters. Each J-16 can comfortably carry 4x PL-17 and 6x PL-15/16. That's 10 long range to ultra long range A2A missiles on each modernised Sino-Flanker. Okay suppose you want to fly faster, higher and longer for those platforms, 2x PL-17 and 2x or 4x PL-15/16. No fighter outside of the F-15EX can do real world and effective air superiority/CAP beast mode as well as the Flanker.
China has an absolute beast of a fighter platform in the Flanker. The Russians just couldn't modernise and digitise their fighters as quickly as the Western and Chinese electronics, computing and software industries move.
The fact that China continues to modernise and produce the Sino-Flanker branches is telling despite having 5th gen proliferation and 6th gen on the horizon. One factor is because China has so much excess productive capacity and resources but if these fighters don't have a place, they would simply retool for 5th gen production. J-16 new blocks, J-16D, J-15T, J-15DT. That's four continuous development and production streams for PLAAF and PLANAF.
My theory on the main utility of modern Sino-Flankers is their ability to carry the larger air to air and air to ground weapons that 5th gens cannot carry internally. Until the J-36 is available in large enough numbers, Sino-Flankers are staying in business.