Scalability always being a problem on cryptocurrency, example like Bitcoin everyone always debate about that. But atleast we already have some solution for that Segwit & Lightning Network. To be honest for future cryptocurrency always make some new progress about their development.
the biggest obstacle in bitcoin is price stability which is always a big problem. because price stability is always a determinant of profits for traders. if cryptocurrencies are made into global currencies to replace the dollar, the standard of currency values is very important, but in the future this can get the best solution.
Price stability is the main problem and there is no concrete tools to fix this issue for adopting cryptocurrency to traditional payment systems.