They don't have to look exactly the same. However, for me, it is important that you can't tell the difference between a UGC and the new case when they are sitting next to each other on a shelf. Otherwise, I will stick with the UGC, not because I like them better, but because I'm sort of commited due to the number I have (especially of the modified NES cases). I don't want to replace what I have. I just want to use the new cases going forward.
That's why I loved the GB/GBC/GBA cases so much. When displayed on a shelf, you can't tell the difference. 
If he's making it the same dimensions as a UGC, then the only really noticeable difference would be the color, unless he makes some clear cases to match UGCs as an option. Otherwise I imagine the difference would be pretty minimal when lined up on a shelf. The rounded edges probably wouldn't stand out on your shelf.
Shadowfox, my vote is obviously go for it. I think the UGC has had its day, but it can be done better with a more premium quality to the design. And you've already proven you can do that.
What I'd be looking for in NES, and later SNES and N64 cases would be:
-Black or dark gray cases like DVD or DS
-Rounded and comfortable to open
-Holds manuals in place
-Holds most official and variant carts in place securely, but easy to pull out
-Can be easily modified to hold any tall or unlicensed cartridges that don't fit otherwise (like Super Game Boy)
So basically your GB cases at a UGC size.
