I understand that one satoshi is very small and for one satoshi to reach $1 a single Bitcoin should be worth over $100 million, but what if that really happens in 30 years or more? If Bitcoin succeds in the long term, this is plausible.

The bitcoin in the transactions on Bitcoin's timechain (aka blockchain) is in satoshis. If you inspect a block, you will find out that all value transfers are measured in satoshis. Currently, there is no way to own a fraction of a Satoshi. It is not possible to own a fraction of satoshi on Bitcoin layer 1 right now because other nodes of the network will reject any transaction that do not comply with the protocol standards (which is to measure value in satoshis). So, if you try to do some fancy thing to own a fraction of a satoshi, it will be reject by the network participants. It seems to me that if one day we need to own a fraction of a satoshi, this could only be done through a hard fork... this is not something we have to worry for the next years, but could be a problem in some decades. This concerns me