Right? That sort of makes it good enough even though I'd rather have it all on the same menu. I'm not sure if the official versions can do that, or at least the latest builds I found didn't seem to. But the mastermod edition from ABZ has an option for "Source flow" which uses the same cover flow as the rest of the UI interface for the boring old source menu. Then it was just a matter of also enabling B to enter the source menu, changing the title for NAND to say "Main Menu" in the config file, and replacing the graphic with one that looks something akin to an app drawer / channel menu. For good measure I also enabled the option to show the source menu at start, so you are greeted with the options to go either way from the beginning.
The Mastermod stuff is BIG with a lot of messy placeholders and misc files and emulator plugins that I couldn't get working properly (I spent hours trying to get covers to display, then gave up because I couldn't get them on the same menu as WiiMC and VC games anyway. I sold out with a snes9x channel forwarder). I just needed the actual app so I could get the source flow thing, and left the rest of it out to keep it lean on my storage card. I think that without all the other plugins and the options removed from the source menu, it actually loads and switches screens ridiculously fast. No loading screens aside from a very brief one at boot.
Again, its not perfect, really I wanted everything together, but its good enough for now.
So someone in another corner of the internet suggested post loader. It does sound promising, but after looking at videos and screenshots of it, I didn't particularly like it visually. On a small screen like a car display, I want big easy to read text and icons like the way wiiflow shows one at a time. Its just extremely clean and sleek looking without all the other on-screen icons too.
I think in the future I might revisit this with the idea of making channel forwarders for all the games I have installed on the USB (there's only like 5 or 6 of them anyway), then I could conceivably turn off the other menus. I think it would be easier than doing it the other way around (making ISO forwarders), right?