Converting your coins to ETH or LTC just for making the payment, and then converting them back to BTC will prove even more costly. Other options include using the Lightning Network for transactions, where the fee is much lower. If you are not using the Lightning, then expect the transaction fee to go up significantly in the future. The fee in terms of BTC will stay stable. But the USD worth will go up, as the exchange rate increases.
That's certainly true, mate. Fee costs will largely depend on current Fiat price and network activity. Imagine if prices continued to soar, as well as, network activity. Bitcoin's fees would've been so high, that only rich people will be able to use it. That's where the Lightning Network comes in. You can easily exchange your BTC to LNBTC in order to enjoy instant transactions at a fraction of the cost. The main Bitcoin blockchain will be used for transferring large amounts of money (like a store of value), while the Lightning Network will be used for everyday payments (like digital cash). If the LN is too complicated for you, then there's always the option of using altcoins on top of BTC for everyday payments. Right now, Litecoin and Dogecoin are ten times cheaper and faster than Bitcoin itself. You can use them as digital cash, while you use Bitcoin as a store of value or long-term investment like Gold.
Nonetheless, I wouldn't worry about the high fees as there many options to choose from that will help you "tackle" this issue. As long Bitcoin remains decentralized, nothing else matters. Depending on your needs, will be the type of cryptocurrency to use for mainstream transactions. The higher the fees, the better it'll be for the Lightning Network and altcoins' level of adoption in the mainstream world. Scaling the main Bitcoin blockchain in order to reduce fees, is not the ideal choice for preserving decentralization/censorship-resistance. It's no wonder why the Lightning Network was created as a separate solution for providing instant, cheap transactions without sacrificing Bitcoin's level of security/reliability. Just my thoughts