Basically you are saying you are not ready for DTS:X yet. And that's fine. I am not fully ready yet either. Though I am a bit more optimistic: I think DTS:X along with Dolby Atmos will dominate new releases in 2-3 years. Perhaps even sooner in the Ultra-HD Blu-ray format.
However, if I were to buy a new DTS:X receiver now (and I just might, within the next few months), then I would be looking for more channels than 7. Here is why.
My current home theater setup is 7.1. And it's not because "more is always better", but rather for some practical reasons. 5.1 would've been sufficient for my small home theater room, but it doesn't work due to the room layout: the entrance in the corner prevents putting rear speakers in the corners. The 7.1 speaker setup works way better for my room.
The main and the most immediate advantage of going with DTS:X (or Dolby Atmos for that matter) is adding the vertical dimension. So, my plan would be to keep my current 7.1 setup and to add 2-4 speakers for height (either in the ceiling or just two speakers above the main ones - not sure yet.) For that I would need at least 9.1 or perhaps even 11.1.
Basically, if you are fine with 5.1 for surround now, then you might be fine with 7.1 for DTS:X, but if your current setup is 7.1 or 7.2 and you want to keep that, you would need additional amplified channels in order to add the vertical dimension.