Is there any plan to add an end game for players mostly done advancing their units?
Once you have all cards to level 100, gold is functionally useless. I have $14 million gold with nothing to spend it on.
Once you have all cards to rank 5, gems are pointless as well.
Adding some extra activities or paths for people who get to this point would be a good idea. You could add overpowered cards, where once you achieve rank 5 you can reset the card to rank 1 again at overpower 1, which adds some more base health and damage for instance. Or maybe unlocks an actual second ability on the card. Or increases attack speed or range.
Or let us sell/trade extra cards over max on a unit to apply to another unit. So we don't have cards that are sitting there with 1000/max.
Just something to keep the game interesting once you are "done" with the initial game, so to speak. I would love more varied objectives or just things to do to give me a reason to keep playing! It doesn't have to be much, just something.