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However, it seems Bittrex is also following the same and there is an IEO on their platform too. Can IEO replace the ICO?
Can you link me to where you saw or read the Bittrexx IEO?
IEOs were already existing before but it has not gained much traction until Binance launched their own. Waves for example also have theirs but it's not that popular. Sure IEOs have their advantages but I do not see it completely replacing ICOs.