If I may put my two cents in, people are going to trade win and multi-accounting to make the most out of their time. This remind me a bit of league of legends where the best way to farm IP (the equivalent to BFP) is to intentionally feed the opponent then afk in the jungle in hope that they end the game within 7-8 min. I expect those who do that to get burnout of league of legends pretty fast. How about simply earning BFP for completing a pvp or pve map. That way multi-accounting or win trading isn't the best way to earn bf and you get to do whatever you enjoy the most at the same time, because, I think, the fastest way to progress in a game should also be the most enjoyable as it is the path most people are going to take. As for keeping people playing the game for longer, implementing new contents (new cards, maps, game modes...) over artificially lengthening the game using a hard cap for BFP is, in my opinion, the way to go.