Polka dot is an open-source project that works with shared protocol that enables Blockchain Networks to work with Synergy. The token serves three distinct purposes; Governance, Staking and Bonding. This is designed to co-exist with Leading smart contract Blockchains rather than competing with them. This is very appealing factor for some Investors. It won't be easy for the Polka dot to challenge Ethereum as many working projects are already using Ethereum Network even though Technically it is superior project but It is already Home of 197 projects those are working on its networks and many more willing to join it.
This is also evident from price movement that we have witnessed during the past month when its price moved from $2 to almost $6 that reflects great interest of Investors in this token. There are some predictions that within a year time , Dot will be Top 3 on Market cap.
We can't deny the fact that Polka has a huge potential to be on top next to Bitcoin but I don't think it could beat or replace Ethereum that easily. It still has a lot to prove and surpass. There were actually lots of coins that attempted to kill Ethereum but none of them became victorious. There will surely be more altcoins that would attempt to beat Butcoin and Ethereum but I don't think they would succeed easily.