A tx now might cost 5k sats, which is approx £2.50.
At £5m per bitcoin, assuming the fee's remain stable, a 5k sat tx now costs the equivalent of £250.
At £50m per bitcoin that tx, again assuming fee's remain stable, £2500.
At that point noone outside of early adopters, business and large institutions are going to make on chain payments.
It's true, sats per vbyte can drop, and they can also rise. UTXO management can also reduce your exposure to higher fee's. But at some price point it doesn't matter what you do, ordinary people will be priced out of on chain transactions.