Can I just say that I think the R9 Nano just needs 4 "real" GB of RAM to have something to offer over the GTX970? That reveal was a small disaster for nVidia, and if AMD can offer 4GB of HBM as compared to the 3GB of GDDR5 (+ 0.5GB backlog cache), that would be a huge thing already.
Also, SINGLE SLOT I/O!!! Can we talk about that for a moment? I've been absolutely disappointed by the amount of cards that still have stacked DVI-ports with the Maxwell GPUs. That completely destroys the point of having single slot WC blocks exist, you couldn't use two cards next to one another anyway. But with the new reference designs all using that layout on the back, you not only get better airflow for aircooled cards, but will also be able to put watercooled ones closer to each other. If we see mDTX boards happen, you could maybe have a quad-crossfire (2x Furx X2 with custom loop) in a Sugo SG13. How cool would that be?
I also have to agree Phuncz on the reference design argument. While the GTX970 reference PCB was already ITX sized, the cooler wasn't, so there was little incentive for aftermarket versions to go the same route. With the R9 Nano, we'll hopefully see a LOT of mITX sized cards with different cooler designs. We need choice in that regard, right now there are 4 mITX sized GTX970s and about 10 GTX960s. If the R9 Nano is on par with the GTX970 regarding performance, mITX GPUs will finally reach a state where they aren't a product for a small niche anymore.