Don't advance when previous keys not up to certain confidence level

[Geert van den Burg]

Hi, I am using keybr to learn to type in russian. But I find that as I unlock new letters, that letter in combination with other letters makes the other letters hard again, and I make many mistakes. I would love it, if first all keys need to be at level 1 confidence, and only then the next key should be unlocked. This also means that the 'current key' or 'focus key' should switch to the lowest confident key to boost that key with the current unlocked keys.

Thanks in advance if this could be made! 

[César Pedraza]

I second this. It would very useful to learn low frequency letters faster.