That's awesome. I was gonna ask if we could see pics of the other side of the board, but I guess it's in there for good now, huh?
Is this something you put together from a development cart, or from a retail cart? (it's in a Yoshi's Island case, so not sure what's going on there) Also, what's the interface for flashing/overwriting new games? Is there software on the pc side you use for file management and writing to the cart?
Also, slightly off-topic, but is your SNES2 modded for s-video out, or are you just using composite? I'm planning to buy a SFC Jr. next month in Japan and later do the s-video mod. If you've done it before I might pick your brain before I heat up the iron. 
Front of the pcb before it got slapped into a case with header connectors:
Yes this is a standard retail yoshi's island cart. I traded my gsu 2 copy of yoshi's island to a friend for his gsu-2-sp1 version of the game. I upgraded the pcb to run anything and everything because I wanted to see if the gsu-2-sp1 does anything special, which it turns out this chip runs just the same. Since I had already wired up anything and everything I figured I might as well slap it into a nice case since this cart can do it all.
There is no "interface" this thing runs standard uv eproms for the gamedata. I just use my eprom burner to program a rom when I want to try it. I could wire up an eprom to flash adapter for flash chips but my burners don't seem to want to work right with a lot of flash chips and I already had these eproms kicking around because of repros I build for people. Nothing is written "to the cart" there's no chip in the cart, the maskrom connections are soldered into that socket at the back and you plug the game rom into that socket on the back to play it. You swap the small chip on the back, and this swaps the game. Swapping the game chip on the back wipes your savedata but this cart is designed just for testing one game at a time. As long as you don't swap the chip on the back any savedata is retained. I wasn't trying to make a multicart because each game overclocks to different speeds so there would be no point in doing that unless you want everything running at the same clock speed.
What you're seeing is s-video from my snes. Here's a comparison of the s-video from my snes jr next to the s-video from a model 1, watch in HD to see the difference more clearly:
https://www.youtube.com/watch?v=K8TcINkc7eEKeep in mind my snes jr is heavily modified, I completely bypassed the original video encoder for a better quality encoder that outputs far sharper s-video and also removes the translucent bar from the middle of the screen. I don't think I even have a guide anymore of how to wire up s-video from the encoder built into the system since by encoder bypass mod generates a far sharper image. The s-video mod I do is way more complicated and wayyyyy more work, there should be lazy instructions somewhere on my forum. All the best mods require a lot of work which usually involves completely rebuilding the circuit, which is what I did in this snes jr.
