You have better also read what satoshi said about trust-less systems.
It is disappointing, when I see people doing the same mistakes, again and again.
You should avoid obeying to a trustee, or being a trustee.
"A trustless system is one that does not depend upon the intentions of its participants, who may be honorable or malicious. The system functions in the same manner regardless of intentions."
You argument is invalid.
Nobody said multi-currency wallets are a prerequisite. People will be taught about cryptos, and they will choose their favorite one.
Then the merchants can easily adopt multicurrency services like CoinPayments.com