I think the mechanical simplicity is very appealing, there are losses in a transmission, but just a chain to motor can be very efficient. But a gear or two would come in handy if it were efficient and inexpensive and not too bulky for a motorcycle.
I've been wrestling with some two speed ideas, hoping to avoid bulk/expense/losses. It gets a little complicated when you add those parameters in.
A motorcycle trans is not compact, after you shoehorn batteries and motor and whatnot on the bike. It is also overkill, the torque curve of an electric motor doesn't benefit from all those gears, only a couple are needed, and the extra gears are just spinning and turning your electrons into heat.
What I was thinking of was a motor with a through shaft, a bike with two sets of sprockets and chains (different ratio on each side), and a clutch on each end of the motor to engage that side, and maybe a one way sprag on the low speed rear sprocket so that you don't have to turn both chains while cruising in exchange for a loss of low speed regen performance.
EDIT, my ETEK showed up today
