It would be pretty easy to modify the Game Gear one for Eurpoean DS case sizes. Since they are clear cases, but have enough stuff on them that a picture wouldn't look great, these would work perfectly for them. In the same vein I intend to have my Sega CD and Saturn games in clear DVD cases to match my UGCs and EU DS cases, so these would again work very nicely.
Great idea for use with DVD cases! I'm definitely going to modify the Sega CD insert for that in the near future. And I might try my hand at a DS insert for Game Gear games as well.
Not long ago I printed off some of my inserts and tested them out on the only 2 UGC-style cases I have. I'm fairly pleased with how they turned out. Here are some pictures (try to look past the surprising amounts of dust inside the cases):







I like how the red turned out and LOVE how the purple turned out. The last picture here gives a really good idea of how the inserts look in person and I'm really pleased with them.




However I wasn't happy with the 32X inserts, and I think mostly it has to do with the fact that neither the orange or yellow template we have really match up with how the retail boxes look. But, that being said, the darker insert looks good with the orange template. I was disappointed in how the yellow turned out though.
There is something some of you might have immediately noticed. These cases are older models of UGCs, and I think the biggest difference is the way they are designed to hold SNES games. The cases I have use two vertical walls instead of the horizontal ones that contemporary UGCs use. The reason I bring this up is that I think the SNES cart holders of current styled UGCs might be directly on top of the text on my current inserts, and that might be obstructive, so I may need to lower the text a little bit on the inserts. If I made a couple of ink friendly test inserts would anyone here mind printing them out and testing them in their UGCs? If so, that would be really swell and I could get the ball rolling on Saturn and black grid Genesis inserts