I'd like to hear some input from current flash cart owners on how their carts work in comparison to this concept: Do they have some cheesy menu when you turn the system on, or can they boot straight to game? Can you leave the USB plugged in while the system is turned on (obviously not transferring to, just plugged in), or do you have to disconnect it? How do you transfer to it? Can you rename files directly on it (thinking no)? What type of games don't work on it? Etc
Also, if you own any flash cart at all, leave your opinion. If I can't get per game loading, I'm going for the best overall cart.
I've got this weird setup going where I want to transfer a game to the flash cart from a PC frontend, then use a USB controlled power strip to boot that system, so my HTPC & MAME cab FEs use the real hardware instead of an emulator. I'm only using hacked consoles and flash carts because the technology allows me to automate things.
Why am I doing this? Because I need someplace to store all my consoles, so why not use my woody MAME cabinet? If I'm going to do that, why not use a frontend to control them? Might be a good place to store one of these XM29s here, too. Exactly.

I see the Everdrive N64 and SNES have USB support. I contacted the dev to find out if you can leave the USB plugged in while the system is powered up, but my guess is a switch will be required. I like that they use SD cards, because I'll be doing a lot of writing to it, which will eventually make it go bad. Unfortunately these have essentially what I'm considering a nag menu, but at least it leaves you on the start game menu function every time. Obviously I really hate emulator and flash cart menus.

Also, lots of these carts just use SD cards, so I bet I could share an SD port with a PC, and then turn it off before the system is turned on. Dreamcast, Sega Genesis, NES, all have SD card carts, but no USB.