In case Bitcoin can be reaching the $2.5 million level of price, surely there can be a good spike of millionaire, but I don't think that it can create or will be the catalyst for a runaway inflation as not all will be converting their Bitcoin to cash and not all holders are residing in only one country.
There will be a lot of millionaires but most of the goods and services have already inflated by that time.
I just can't see 50% of the world's population being millionaires.
Do you have a valid source for that estimation of potential millionaires in the future with that percentage because of bitcoin? Just like the theory that bitcoin might become $2.5M in the future, you're also having a theory about the number of potential future bitcoin millionaires. There will be massive selling from $100k-$500k at that point of them and most likely, many will sell all of their bitcoins at that range.