Cardano replaces Ethereum?
Cardano is one of the coins that has good potential, but I think the competitor closest to Ethereum is EOS. Even so Ethereum has reacted with these issues by releasing Ethereum 2.0, Ethereum is still very popular now with the support of the community and ICO who use the Ethereum network.

If Ethereum 2.0 Project runs smoothly I think it is difficult for competitors to replace Ethereum at this time, we wait until the Ethereum 2.0 project is finished and see what will happen.