USB SeatPost Charger Project

You're not missing anything. I used to find on my motorbike that a USB charging slot was so handy when riding - i.e. using a car satnav or charging a phone. I wanted to have the same option on a roadbike, but without the use of a dynamo. Just thinking about all those people running Di2 and EPS with a battery converted to run inside the post - so thought it may be nice have a port on the post for a rear light to charge if it dies on a commuting trip or just to juice something up when moving.

Not really a business idea, otherwise it would be dynamo related - just a slimline or rather bike fitting inside rechargeable power pack

Extended battery life for lighting, good idea. I get that. Charging up the post battery would be part of trip prep, so no extra bother really.

Day-to-day though, remembering to either take out the seatpost to charge it, or plugging the bike itself in would be a PITA unless I was already running Di2/EPS and was in that habit anyway.
Not gonna happen any time soon though - I mean the whole beauty of a bicycle (to me) is that I don't have to fuel it up.

As an aside - Ty from GSC ran a Tout-Terrain 'The Plug' on his Stinner MTB (powered by a SON front dynamo hub) when he rode the Tour Divide this year. Haven't asked him how it held up yet, will hopefully do so soon.