May not be too late. I did play around with adding a second slot. I'm just a bit conflicted. It seems there's a certain number of people that try out these GPU (like the 750 Ti), that aren't completely happy with them. I wonder if I shouldn't encourage people to use these GPU, and instead steer them towards something like the S4 Mini? Those who really want to may be able to de-solder the DVI port (?).
I should probably just stop overthinking it and make the case larger and add the dual slots.
I haven't made much progress in the last month. December was spent waiting on a new anodizer located in Calgary that I had high hopes in. Unfortunately, a month has passed and I still don't have my parts. I can't risk using him for anything else. So it looks like I'm back to powder coating. The current plan is to get a small number (2-5) of final prototypes made in January, make any necessary tweaks and then order a larger batch to finally sell.