I am quite soon through with two of the larger lists. It would be cool to have some kind of secret animation or magical power that is unlocked when you are through with such a long term endevour - maybe after a "boss-level-high-strictness mode"?
You could add those after HSK 1, HSK 2, HSK 3 - and of course after finishing HSK 1-4!1
Just to add to the fun factor. I found that Skritter has pretty much become an entertaining game for me.
No, this is is not of high priority. A feature like Sentence practice / dictation would definately be more importatant.