Exactly, BTC fees are the issue for Bitcoin broader acceptance at this point.
But transactions fees are very low with NEM and MONA so these coins may be more easily accepted by Japanese merchants throughout 2018.
NEM transaction fees is low but in order to obtain NEM, we need to face the exchange withdrawal fees
(deposit BTC > trade NEM > Withdraw). If Im not mistaken, Poloniex, Bittrex have 15-20 NEM fees as withdrawal fees so it's like paying $13-$17 at the current exchange rate. Since there is no direct purchase of NEM available at the moment without dealing on an exchange
(correct me if Im mistaken here), people will have to used bitcoin first then deposit it to exchanges.
Well that is just based on the current status. Who knows in the future, there will be a standalone NEM exchanges where deposit and withdrawals are less cost.