Calculations aside, which fraction do you think will be the main one in a few years, when people don't talk about units in Bitcoins anymore because it is too big and we should add too many zeros?
I think that it depends on the amount of Bitcoin we're considering and also the fraction of Bitcoin you intend measuring. While Satoshi will be good mostly for smaller transactions due to it high level of precision, micro bitcoin on the other hand is mostly suitable for small to medium size transaction and since mili Bitcoin seems to be closer to the traditional currency, it will be convenient for a much bigger transaction.
Will people talk in sats? I think the problem is the contrary but at the same time the same because it would suppose too high numbers which is almost as uncomfortable as adding zeros as in the previous case.
I think that for the sake of putting users into consideration when it involves the use of Bitcoin in normal transaction, it's most likely that
Micro and milli Bitcoin would be the most preferable to use.
Let's take for instance that In the future bitcoin gets to 1
BTC=$100k then
μBTC= $0.1 which is very much easier to make reference to while making any transaction.
If we're relating this to mili Bitcoin, then if
1
BTC=$100k then
1 mBTC=$100 which is what's conversant with most people.
Apart from the precision that the use of Satoshi might profer, in terms of usability and convenience, μBTC and mBTC will work well in the future when Bitcoin becomes too big a value and gains the level of adoption that could make it possible to do most transaction with Bitcoin.