GC does help with ABA style concurrent problems, and it also simplifies the places where you simply don't care (slow/uncommon paths). But concurrent data structures are a special case, and likely, not always the best anyway since even though they scale much better than locks, with enough writers and cores, the cache coherence traffic is going to swamp the application.

I do agree with the flexibility comment. A hybrid environment where you can pick and choose the mem mgmt strategy (and, very important, not pay in perf for things you're not using) would be great.