I don't see ETH becoming a scam due to increased centralization, rather it will become more controlled and subject to regulators. This would result in the end user having their coins censored and blocked at any time for political or other reasons. This is definitely not good for cryptocurrencies in terms of their fundamental properties. For speculators and traders it will not turn into anything, they don't care what they trade with, no matter if it is centralized or decentralized coin. The main thing is to have volatility.