RX480 with 4GB GDDR5 are $199. I don't know how much other stuff that you need in the dock would cost but seems they could come up with something competitive next year if they wanted to.
The RX 480 is assumed to be what's going inside the Neo, so if Nintendo could pull off a combined package of $400 (the expected price of the Neo), this would pretty much be a way to compete directly in regards to power, while providing additional functionality for the cost. Then again, they could also go for something lower (RX 470) for less, and still have a decently powerful home console that would be relevant to developers.
I'm not sure what the best solution for RAM would be in this scenario, and I can't seem to find accurate costs for LPDDR4. However, DDR4 seems to be getting less and less expensive, so I suspect the RAM wouldn't be a huge extra cost, but I could be mistaken.
Also, in regard to marketing the console, I just had an idea of how they might market the SCD...
I completely forgot about the VRAM that comes with GPU Cards. I was stuck thinking of a configuration similar to the PS4.