Not really an answer… But this sounds a lot like the past beta feature called ‘leech detection’ which fell by the wayside, I think it was superseded by the development of the iOS and HTML5 apps. But anyway, it’s certainly possible and so maybe they’ll think about bringing it back?
See previous posts:
To take it further, this might actually kind of be related to this suggestion below; leech characters could be shown in the context of words they occur in:
Thanks Catherine, you obviously know your way around this forum!
This feature would definitely get my +1 if there’s any developers reading this - there are some characters I’ve been learning for 7 months that keep popping up and it would be nice to isolate them easily and nail them down once and for all.