Let's remember that the IL-76 is a lumbering and outdated aircraft and does not compare well with the likes of the C-17 Globemaster which can easily clock 30,000 hours without a life extension programme I very highly doubt that IL-76 can do the same
Even with a full glass cock pit, upgraded avionics and a new engines it's still not good enough to compare with a true heavy lifter like the C-17 or the Y-20 for that matter, as a matter of fact I would also find it hard to beat a C-130J
Don't look down on it that much. It is a capable heavy lifter. And it is the ONLY heavy lifter that China has right now.
It's the IL76s that are modified to turn into KJ2000s.
It's the IL76s that flew to Libya to carry our fellow countrymen back in times of crisis.
It's the IL76s that flew to Perth to search for debris of MH370.
Now it's the IL76s that are providing strategic air-refueling capabilities for the PLAAF.
As of now, NO other aircraft in the PLAAF inventory can do any of the above tasks. And NO other similar aircrafts (C17, in this case), can be readily bought by the PLAAF. And NO other indigenous aircraft (Y20) is readily available for production at this point.
As much as there are drawbacks of the platform: lifespan, engines, ageing airframe for some refitted ones, a small diameter body as compared to C17 and Y20, it still is and will still be the ONLY heavy lifting platform that PLAAF needs so badly in years to come while the Y20 is tested and developed.
As much as C130J is a very capable and very advanced tactical transport aircraft, it simply does not perform and are never meant to perform the roles of a IL76. Another thing to bear in mind is price: we paid 44 million USD for THREE IL78s, meanwhile ONE C130J costs 60 million USD and even if we are willing to pay, we can't.
Furthermore, I doubt a long lifespan will be of a lot of importance to the PLAAF. Y20 is in the works and with the planes being this cheap--it simply does not matter that much. Even if there's only a few years of lifespan left, it's still needed and worth to pay at this price--at least that's how I see the PLAAF deems it so.
After a few years the Y20 would be ready, even if the early version is going to be fitted with D30 engines, so the drawbacks really don't matter that much in lieu of this.