A hybrid would well-suit the replacement of these. Something like the Chevy Volt that relies more on electricity for heavy stop/start type driving. It would also address your concerns. The engine could just run when needed to charge, and not be a constant oscillation through the RPM range through the neighborhood.
1 - https://en.wikipedia.org/wiki/Grumman_LLV
A hybrid would well-suit the replacement of these. Something like the Chevy Volt that relies more on electricity for heavy stop/start type driving. It would also address your concerns. The engine could just run when needed to charge, and not be a constant oscillation through the RPM range through the neighborhood.