Those covers look really nice and site-worthy!
By the way I'm also 100% for DS and older stuff in DS cases only 3DS in 3DS cases!!!
Thanks for the vote of confidence.

I've submitted them for consideration; I hope they get approved.
For me, the biggest draw for using 3DS cases would be the fact that original GB carts fit inside without any trimming needed (although they do need spacers to be stored properly). And although trimming DS cases isn't necessary for GBA games (assuming you're putting them in the old-style DS cases), fitting the instruction manuals inside still requires some trimming on the inside cover. I haven't yet dedicated my handheld collection to one format or the other; all of my GBA games are still in their original boxes where applicable, and all my old GB games are safely tucked away in a box. I'm still not sure which route to take.
I may just keep to this format as well, but the 3DS cover template is very nice and is set up in a such a way that re-sizing back covers no longer becomes an issue. There are tons of covers for GB and GBA alike that suffer from the re-sizing issue, and not having to worry about that anymore is an attractive prospect. I think I might put together some kind of hybrid of the two, unless its creator/s beat me to it.