The new variety of rocket engines in 0.7 is awesome. I would like to see more incentive to right-size the rocket for the mission. Right now, a big rocket can magically operate at 1%, and reignite over and over with 100% reliability.
Maybe deep-throttleability and reignitability should be options that can be added at a cost in $ and mass.
These tradeoffs could apply to jet engines, too. SR-71 relied on shots of Triethylborane (TEB) to restart it's engines in flight, and they carried a limited quantity onboard.
TEB was also used to ignite Saturn V's F-1s and Falcon9's first & second stages.
@Kell Like the space shuttle main engines, if I'm remembering correctly!