Dynohub, with battery/capacitor integrated (at the hub, the weight shouldn't be an issue) for maybe 5 minutes of 5V regulated USB power, and a line coming off with some ability to tap into it for parallel USB ports wherever they're needed.

Essentially, I want something that will charge some USB-rechargeable accessories, but not have the annoyance of them kicking out of charge mode when I stop at a light or sign and then back into it when I start off again. At least for my phone, that could be really obnoxious (losing the "screen always on when charging" for example - interestingly, the phone only seems to care that it's getting 5V; current determines how fast it will charge if at all, but 5V at <100mA keeps it in the charging mode so the screen stays on) and with all the GPS-based apps, it pretty much eliminates the need for a cyclocomputer if I could just keep the battery from dying so fast. Standardizing on USB means it can charge any of dozens of headlight/taillight options that are almost always cheaper than (or at least comparable to) direct dyno lights. (And having them use their own batteries lets them deal with any high current or odd voltage requirements internally.) Charging (ideally with passthrough capability so they're charging - or at least offsetting some discharge - during use) rather than driving them directly means you could charge someone else's lights for them, or use your headlight as a flashlight off the bike, charge a helmet mount light etc.

More fun; add an alternate power/storage option so that a larger USB power pack could be added to the system, sinking or sourcing as conditions dictate, and/or "shore power" to charge everything up from an external supply when parked.