The problem with that is processing power. If the Echo could do speech to text without the cloud (such as generating that transcript you mention), then it wouldn't need the cloud in the first place.

I'll give you that it could be possible to slip in other "trigger words" that could be tallied, then statistics sent off, but really, is that a problem? So what if your Echo counts how many times you say a specific keyword? Would that affect your life in any way?