Well, I guess if China is going to fight a low-med intensity conflict in wich it's modern fighter force should be able to optain air-supremacy rather quickly, even an old H-6 has it's merrits. It provides a large payload and a loiter capability, combined with guided munitions, if integrated, that allows for a timely engagement of targets of opportunity, that pop up and disappear again.
The US is still using it's B-52s, for the missions in Iraq and A-stan absolutely enough.
And I believe you can still train and develop tactics and employment procedures with these aircraft, so that when PLAAF transitions to a newer airplane, the knowledge is still there.
Regarding big stealth UCAVs, I think that's still way into the future. After the J-8s, China went all the way through the process of building J-11 and J-10 like aircraft to end up being able to produce some kind of a fifth gen fighter at some point. Even with the know-how acquired there, I doubt they could really leap frog all the technology in between H-6 and a stealth UCAV without big problems.