They really can't do anything about the texture pop in. The bottleneck lies in the fact that they're streaming texture data off of the game medium rather than straight out of RAM. If you install the game to your HDD then it will be much improved, however.
I agree with you in that Rage had some great gun mechanics. In fact I think it had some of the most refined gunplay of any game I've ever played.
As for the DLC, that wasn't just a rumor. Since Rage's release id has been working on a lot of different stuff for DLC. But when Rage first came out, DLC wasn't a top priority, and that was made even more so when id started getting backlash for all the technical problems that Rage had at launch. Following that all of the WIP DLC was put on the back burner and only now that the whole issue has begun to calm down are they really getting back to it.