Power through flash hotshoe
I'll be moving soon to the Canon 5D camera from my 20D. It's better in just about every way, but like many "pro" cameras it does not have a built in flash.
It's not that there isn't a reason for this. Built in flashes usually suck, and nobody would use them for any sort of serious photography, except for fill. So if you're going out on a shoot, you would of course carry along some quality flashes and the built-in would be a waste of space.
On the other hand people use cameras like the 5D and 1Ds for more casual shooting, and if you don't bring a flash and you find yourself wanting an indoor shot, you may find yourself out of luck with your multi-thousand-dollar camera. And, as noted, there is the need for fill. Pro flashes are big and unweildy, you don't strap them on if you don't need them.
So here's a compromise. Add lines to the hotshoe for power, with a smart power bus that only applies real power when a smart flash is confirmed in place, and communicates digitally about voltages and current levels. This would have several benefits.
First, one could sell a small add-on flash that needs no batteries, it's just capacitor, controller and flashtube, no more than the built-in flash used to be, but perhaps on a telescoping stick so it can raise up high over the camera as a flash should. In fact the camera batteries are pretty powerful, so you could consider making this a decent flash, at the cost of sucking your camera battery faster. But why not? Why not just carry more of one type of battery rather than having two different types for flash and camera? In addition, some people use a special grip on the camera that holds extra battery power.
This power bus could actually even have value with a flash that has its own batteries. You might elect that when those batteries get too low, you could switch to internal batteries. If it means getting a shot that you could not get due to dead flash batteries, of course this is worth it. In Canon cameras, internal battery is 7.2v and flash uses 4xAA meaning 6 or more likely 5 with NiMh, but a flash can easily take this range of voltages. (A fancy camera power supply might even be able to work in reverse, sucking power from the flash batteries when the camera battery is the one dead.)
Of course, I still want all the other goodies I've asked for -- making infrared flash control standard in the camera bodies, instead of a $200 add-on. (At least with the power available the add-on transmitter could be smaller and cheaper.) And the dream we'll never get -- some standarization among vendors.
This power bus could also power other things -- GPS receivers, radio transmitters, audio recorders, portable microdisks, anything people can think of.