This is the chart of Bitcoin's Avg. Transaction fee:
https://bitinfocharts.com/comparison/bitcoin-transactionfees.htmlRight now the median fee is about $2. After lots of halvings the reward won't be enough to satisfy the miners. I guess that after a decade, bitcoin will be more widespread, as a result, more transactions will occur every second. Won't this increase the median fee? If it does, bitcoin will start being a not-so medium of exchange. Imagine paying $5 for a transaction. Even paypal doesn't charge that much.
I guess that actually depends on the transaction fee's being set by the exchange or whatever is holding your Bitcoin. $2 is already a big amount in some countries and that would already be equivalent to a meal. It would be expected for these transaction fee's to grow since higher value of Bitcoin takes more time to transfer and there are some options that allow you to rush transactions by paying higher fees.