We should all be so lucky that some other languages are willing to break backwards compatibility. Even C++ gurus like Scott Myers advocate that language finally breaking source compatibility [0]. Often, breaking compatibility is the only way to make a language better.

[0] http://scottmeyers.blogspot.nl/2015/11/breaking-all-eggs-in-...

Swift is a young language. That it breaks some things now means we won't be stuck with its early mistakes forever in ten years.

Yes. But everyone cares about their code base which they have today not after what they are going to do in 10yrs. An asteroid could wipe us all tomorrow. So I'm definitely worried about reworking stuff that I already wrote.

Demotivating only if you've ignored the many public discussions about how this was going to be the case.