PMS | LEVEL 100 MAGIKARP
re: fidi controllers.
there's a local guy who made himself a fidi after i told him about it, and so i asked him if he could make me one, just because they're cool. he said he was working on a new schematic that took all the buttons and put them over as actual buttons, and swapped the csitck into a set of 4 buttons, as well. then, basically just use a normal fightstick, converted to read analog, as the left analog. in theory, it'll work out well, unless you're playing melee where light press shields matter (i don't think they do in sm4sh, but i could be wrong), and further in theory, if light shields matter, it might be possible to set one of the shield buttons as a light press (though, that might need to be a mechanical fix...).
he doesn't have the schematic done yet, so i don't know how it'll look (might be too busy on the buttons side...) and i think he's still trying to tune down how to properly analogize the stick, but this sounds interesting. i think he actually independently addressed some of the issues you had cited yourself with the fidi design, and i know i wasn't thinking of cstick converted to buttons at all.
i'm guessing you can actually angle your smashes with the cstick, if you use it as such, but i don't pay much attention. that's the only real drawback i can come up with off the top of my head to that setup, other than the fact that the right side is going to be suuuuuuuuper busy with all the buttons going on over there. might need to start employing multiple sizes or something...