sdio looks like the best bet from what GPH has said so far - I would have really liked to have seen a USB host port on the device since given it's running a linux kernel this would have made using a wifi usb adapter trivial. I've read somewhere that GPH is thinking of releasing another version of the GPX2 with USB host but that's just a rumour.
Mmkay, that's a shame it would be nice to have a real-life GP buddy to share the fun of the new console when it arrives (and if it's any good, i.e. what will determine whether or not I get one)
if its like on the gp32, the chip fully supports host mode and you can switch it to that, what you just need is 5v for the power.
i made a small box with 4xrechargeables and 2 female usb connector for the gp32 and used it for gp32linux, worked great! the wifi pack is awesome.
anyway, i hope this is possible with the new gp32 too, but for that we need a whole new system kernel i think.
Man if this thing can some how be connected to a wifi access point and runs linux that would be amazing. Just imagine a small device that could be used to connect to a mythtv backend to watch live cable tv. My laptop works well for this right now. I can get live cable tv to stream to it wirelessly but if I had something pocket size that would rock.
If it does support WiFi through SDIO, I might actually consider getting a WiFi card; I could use it both with my Zodiac and the GP2X (if I get one...).
Other SDIO accessories should be possible to use as well, like a camera or something...