Making an ion-only plane was perfectly possible before, and not even very hard: There was a whole challenge thread here if you're interested: http://forum.kerbalspaceprogram.com/threads/26137-Challenge-An-aircraft-capable-of-flight-using-ion-engines/ The only thing the new ion buff made was to cut down the time burn time to get anywhere down. That I think is a good thing, since I've never used the stock ion engines on a space craft before, they were so uselessly slow to get anywhere. I don't fully agree with the decrease of electricity usage though, that should've been quadrupled along with the thrust.