ICX usage is not only limited to transaction fees. You can do an ICO with ICON and pay with ICX to buy goods or services within a DApp. ICX can be used to pay inter-blockchain services between blockchains connected via Interchain.

It is possible to gain virtual step by staking, and earn incentives through IISS. Virtual Step is also available for SCORE interactions, so ICX will still be required to pay step fees in other types of transactions.