One of the biggest challenges that we will encounter in Bitcoin is the Scalability problem which means there is only limited amount of information that can be contained or its capacity. I'm sure that there will be more people who will going to join the campaign which will result to a possible delay during processing or trading. So how can we provide a solution on this or how to ensure that all the trading done were saved once delayed before bitcoin achieves mainstream adoption?
Yes this is one of the biggest problem of the bitcoin because the transaction cannot be done instantly so if it need to be considered as a mode of payment the transaction should be fast but it is not possible in bitcoin but the transaction speed increased a lot better when compared to the past years so in future the this will get more improved after the implementation of LN and it may make the bitcoin transaction at much faster time.