5 Amps is too much for the standard cable and will require safety considerations such as additional pins, available only on compatible thick cables.
I don't think it's a good idea having 5 amp connection. It's like a gently 1 KW barbecue grill and desperate housewife's desperate iron connected to the standard power outlet - it's unsafe: think about all the problems with overheating, contact problems and sparks.
Also, this standard can be implemented only on new desktops - none of the mobile computers will provide quality ports capable of such current and none of them will have additional 100 watts of power in reserve in case of use of battery and even for power supplies - their size will double.
How many devices, requiring such power have you ever seen? Monitor? Is 16-24 volts a good idea and enough?
I think better idea is to introduce 48V power in modern power supplies:
-> It will provide 100 watts of power using 2 Amp cables - smaller footprint and more safety
-> 48 Volts is a good option: this voltage is "standard" and used in many devices and you can easily get 24 from it, much easier than 48 from 24, it's efficient :)
Dunno, I think this USB guys are bringing new ideas and are not ready to finalize standard, yet...