I never said C3 must go opensource after those "5 years", only that it could go to normal license, provided that Scirra has moved on to new versions for main income, so to say?
It is normal for old versions (and there's newer versions) to get cheaper so this might be the way for subscription software that get old and replaced with newer versions, these could get new type of license..
But yeah, it is really up to Scirra this whole thing.