I absolutely want to see a good how-to on a mod that installs some L2/R2 shoulder buttons to the provided contacts on the board, preferably something low-profile that isn't going to jab me in the leg or poke holes in my pockets. 'C' and 'Z' buttons I could take or leave, however PSX was the first with the L3/R3 clickable analog sticks, and a few games started using them that early. Those I'll probably map to the keyboard somewhere close to the nubs.
IR has some potentially interesting uses. As a "How To" mod it would be nice to have (I have a Robosapien that runs on an IR sensor) but I can take or leave it.
I'm not big on cameras, however hardware that is "Video-Ready" seems to be the standard at this point. I think if the OP team was planning an upgrade to the hardware DSi-type cameras would be necessary just to meet the baseline expectation.
The flashy lights I can do without. A pretty case is nice and if it was a desktop or had a few days worth of charge-time I'd be interested, but they chew up the battery and I need my 'hours in operation'.
My $0.02.