Currently Kanban board only counts number of cards in column per swim lane and each card is value of 1 point. It would improve Kanban board usability if you could also add custom point value per added card. Point could represent hours or just relative effort estimate.
Points could also be implemented as special tags added to cards or postit notes. E.g. tag with name “2 points” or “points=2” could be counted. This would not introduce any new functionality but would reuse of existing features.