The UI is pretty much unchanged. Workflow no longer requires you to add images to a project before working on them - you can work directly from a folder of images, export sidecars and convert. Biggest improvement is that the image processing is much faster.
While that sums it up, I'd rate the UI as a significant improvement. I hated the project requirement previously as it added nothing for me and only took extra time to click through it. Speed improvement for CPU only wasn't significant to me, but the GPU support made a huge difference.
Processing 21 random 7D RAWs with supported lens modules:
V6.6: 234 seconds
V7 CPU only: 201 seconds (1.16x speed of V6.6)
V7 OpenCL: 88 seconds (2.66x speed of V6.6)
My hardware: i7-2600k stock, 8GB ram Win7-64, HD6850. So I do have a relatively fast CPU with a current mid range GPU. If you have a slower CPU and faster GPU the relative improvement could be much greater.
On adding cameras, you'd have to look at the history for an indication. For example, v7 brings support for the Sony a77, NEX C3 and 5N, Fuji X100 and a Nikon P7100.
On adding modules, I don't think anyone can give a definite time scale. You might be able to influence their priority list by filling in a form
on their web site.