One thing about Q-5 vs. WZ-9C/10 is that while both will accomplish the same ground support, both operate from different branches, so they are not in a sense comparable. Just like A-10 vs. Apache.
Like the USAF, anything that has wings falls under the Air Force.
But if it has a rotor on it, then it's the Army that controls it.
The Q-5 is there because China does not have a dedicated CAS aircraft like the A-10 or Su-25. The thing is, it may not be wise to develop such a dedicated CAS plane when the future of this very niche itself is being questioned.
The Q-5 will go on and on filling that niche until that niche becomes obsolete, and in that sense, it won't be replaced. In the end, the Q-5 will die with that niche.
On the Backfires, not too long ago there is this story that Russians won't sell the plane to China because they feel threatened about Chinese in their borders with Backfires. Now they're banging on China's door when China is no longer interested?
Also China won't buy Backfires for the same reason why China junked all their variable wing geometry projects in the first place. Yup, you guessed it.