The industry is stagnating because everything is controlled by massive publishing companies who are obsessed with name-brand franchises and forcing developers to churn out full-productions annually. I think the majority of industry issues would resolve themselves if publishers would just slow the f@ck down. DLC is a powerful tool that's being underutilized. In my opinion, Gearbox did it right with Borderlands. When the game was a hit, rather than just rush straight into Borderlands 2, they put some effort into their DLC (new quests of decent length, new items). This allows the both continue the franchise, recoup their costs, but doesn't require massive amounts of investment into development. If done properly, it also allows the community to build around a game and enjoy it for a solid period.
I just think the Activision model is too fast. You play Modern Warfare 2, and then a year later Black Ops is out, and then MW3 a year after that. And the DLC is garbage. They're map packs. No new Spec Ops missions, no new campaign expansions. It's a low-quality product rushed for a quick buck.
Modern games are expensive, with high-production values, engine costs, etc. We get it. So rather than rush ahead, distribute the costs. Microsoft and Sony recoup their costs on console R&D by selling the damn things for seven or eight years. Epic licenses their Unreal Engine, iD used to do the same with their iD Tech to regroup their development costs. Rather than rush from sequel to sequel, they focus on smaller, quality expansion packs running off the same tech. Then again, the last three Call of Duty games have basically run on the same engine, so I'm not really sure how they're racking up such a bill producing them (marketing aside).