NodeBB is still **0.**x, so it's not released yet. This is why I don't keep backward-compatibility.
Because if you use software that isn't released yet you are a guy who doesn't care as much about stability as those who use released software only. Therefor you are one of those who stay on bleeding-edge of software. So there is no reason to keep backward-compatibility for those guys.
And as long NodeBB upgrades don't break the old database-content you can update your NodeBB system without problems. If this wouldn't be the case I'd reconsider my thoughts about backwards-compatibility.
Another point is that 0.6.0 breaks some plugins because of renaming of hooks, which would (didn't test it) cause plugins keeping backward-compatibility by containing the old hooks throwing deprecation-warnings on NodeBB-start
but according to the "Plugin/Theme Dev" Group on this board I'm not a plugin-dev, so you can just ignore this ^^ So you now have to consider me as plugin-dev Thanks @julian