You can always use 1 satoshi..
but if price really increases that much.. it might be possible that 1 satoshi becomes the "standard fee".
But of course 1 satoshi will get divided into more decimals.
even with the theory that the bitcoin valuation will increase. is meaningless.
here are the reasons.
bitcoin has increased in value 10x since a transaction fee was below 1cent. so do you think the amount of satoshi's needed should be 10x less to keep the fee below 1 cent.. well the answer is that it should. but instead, it has not. and infact the average transaction fee is now about 15cents to assure next in line priority.(over 20x the value it was before)
and as for imagining the far distant future where pools are only mining 0.78125btc a block in the year 2032... this still will not be an incentive to lower fee's
as the pools will start to want to be subsidized (currently fee's are not treated as a subsidy, and just a bonus. but in 2032, that will switch)
another reason is. that if in 2017 we will allow approximately 7500tx per block. we could see 15,000tx by 2020 30,000tx by 2025 and 60,000tx by 2030
so imagine all these lightning network hubs combining 60,000payments of just 1sat fee. to create a large LN settlement transaction fee of 0.00060000 (imagining LN was charging just 1sat per user) for anyone else to want to make a REAL onchain bitcoin transaction they will need to pay 0.00060001 as a minimum just to outbid LN.
so the short answer to the very distant future scenario is
bitcoin transaction fee's would be higher in the future, but no one will care because they would be pushed to the less secure(but cheaper fee) hubs due to these new layers and price war of onchain fee's
even shorter answer
bitcoin fee's will not be 1sat. but second layer hub transactions could be