ebike kit from shimano

Potentially interesting - an integrated kit of stuff you need to make an electrically assisted bike from a major manufacturer.   The market is rapidly maturing. 

250 watts is just fine for a human/electric hybrid.  There is no reason to build escooters.  If you have a utility bike in a place like San Francisco, 500 watts may be more sensible. but for the vast majority of bikes they are doing the right thing.