Some modern electrical solutions seem to be very near this ideal. Take a look a Mahle, their rear hub motor and small in-frame batteries only seem obvious I you take a close look.
(What I'd love to see are more cheap bikes and bike components. I'm currently searching for an “acoustic” commuter bike and I find solid bikes are rather soon outside my preferred budget.)
https://mahle-smartbike.com/ebikes/
(What I'd love to see are more cheap bikes and bike components. I'm currently searching for an “acoustic” commuter bike and I find solid bikes are rather soon outside my preferred budget.)